| Message ID | 55E82AFF.4020401@arm.com |
|---|---|
| State | New |
| Headers | show |
On 03/09/15 12:11, Andre Vieira wrote: > On 01/09/15 15:01, Richard Biener wrote: >> On Tue, Sep 1, 2015 at 3:40 PM, Andre Vieira >> <Andre.SimoesDiasVieira@arm.com> wrote: >>> Hi Marc, >>> >>> On 28/08/15 19:07, Marc Glisse wrote: >>>> >>>> (not a review, I haven't even read the whole patch) >>>> >>>> On Fri, 28 Aug 2015, Andre Vieira wrote: >>>> >>>>> 2015-08-03 Andre Vieira <andre.simoesdiasvieira@arm.com> >>>>> >>>>> * match.pd: Added new patterns: >>>>> ((X {&,<<,>>} C0) {|,^} C1) {^,|} C2) >>>>> (X {|,^,&} C0) {<<,>>} C1 -> (X {<<,>>} C1) {|,^,&} (C0 {<<,>>} C1) >>>> >>>> >>>> +(for op0 (rshift rshift lshift lshift bit_and bit_and) >>>> + op1 (bit_ior bit_xor bit_ior bit_xor bit_ior bit_xor) >>>> + op2 (bit_xor bit_ior bit_xor bit_ior bit_xor bit_ior) >>>> >>>> You can nest for-loops, it seems clearer as: >>>> (for op0 (rshift lshift bit_and) >>>> (for op1 (bit_ior bit_xor) >>>> op2 (bit_xor bit_ior) >>> >>> >>> Will do, thank you for pointing it out. >>>> >>>> >>>> +(simplify >>>> + (op2:c >>>> + (op1:c >>>> + (op0 @0 INTEGER_CST@1) INTEGER_CST@2) INTEGER_CST@3) >>>> >>>> I suspect you will want more :s (single_use) and less :c (canonicalization >>>> should put constants in second position). >>>> >>> I can't find the definition of :s (single_use). >> >> Sorry for that - didn't get along updating it yet :/ It restricts matching to >> sub-expressions that have a single-use. So >> >> + a &= 0xd123; >> + unsigned short tem = a ^ 0x6040; >> + a = tem | 0xc031; /* Simplify _not_ to ((a & 0xd123) | 0xe071). */ >> ... use of tem ... >> >> we shouldn't do the simplifcation here because the expression >> (a & 0x123) ^ 0x6040 is kept live by 'tem'. >> >>> GCC internals do point out >>> that canonicalization does put constants in the second position, didnt see >>> that first. Thank you for pointing it out. >>> >>>> + C1 = wi::bit_and_not (C1,C2); >>>> >>>> Space after ','. >>>> >>> Will do. >>> >>>> Having wide_int_storage in many places is surprising, I can't find similar >>>> code anywhere else in gcc. >>>> >>>> >>> >>> I tried looking for examples of something similar, I think I ended up using >>> wide_int because I was able to convert easily to and from it and it has the >>> "mask" and "wide_int_to_tree" functions. I welcome any suggestions on what I >>> should be using here for integer constant transformations and comparisons. >> >> Using wide-ints is fine, but you shouldn't need 'wide_int_storage' >> constructors - those >> are indeed odd. Is it just for the initializers of wide-ints? >> >> + wide_int zero_mask = wi::zero (prec); >> + wide_int C0 = wide_int_storage (@1); >> + wide_int C1 = wide_int_storage (@2); >> + wide_int C2 = wide_int_storage (@3); >> ... >> + zero_mask = wide_int_storage (wi::mask (C0.to_uhwi (), false, prec)); >> >> tree_to_uhwi (@1) should do the trick as well >> >> + C1 = wi::bit_and_not (C1,C2); >> + cst_emit = wi::bit_or (C1, C2); >> >> the ops should be replacable with @2 and @3, the store to C1 obviously not >> (but you can use a tree temporary and use wide_int_to_tree here to avoid >> the back-and-forth for the case where C1 is not assigned to). >> >> Note that transforms only doing association are prone to endless recursion >> in case some other pattern does the reverse op... >> >> Richard. >> >> >>> BR, >>> Andre >>> >> > Thank you for all the comments, see reworked version: > > Two new algorithmic optimisations: > 1.((X op0 C0) op1 C1) op2 C2) > with op0 = {&, >>, <<}, op1 = {|,^}, op2 = {|,^} and op1 != op2 > zero_mask has 1's for all bits that are sure to be 0 in (X op0 C0) > and 0's otherwise. > if (op1 == '^') C1 &= ~C2 (Only changed if actually emitted) > if ((C1 & ~zero_mask) == 0) then emit (X op0 C0) op2 (C1 op2 C2) > if ((C2 & ~zero_mask) == 0) then emit (X op0 C0) op1 (C1 op2 C2) > 2. (X {|,^,&} C0) {<<,>>} C1 -> (X {<<,>>} C1) {|,^,&} (C0 {<<,>>} C1) > > > This patch does two algorithmic optimisations that target patterns like: > (((x << 24) | 0x00FFFFFF) ^ 0xFF000000) and ((x ^ 0x40000002) >> 1) | > 0x80000000. > > The transformation uses the knowledge of which bits are zero after > operations like (X {&,<<,(unsigned)>>}) to combine constants, reducing > run-time operations. > The two examples above would be transformed into (X << 24) ^ 0xFFFFFFFF > and (X >> 1) ^ 0xa0000001 respectively. > > The second transformation enables more applications of the first. Also > some targets may benefit from delaying shift operations. I am aware that > such an optimization, in combination with one or more optimizations that > cause the reverse transformation, may lead to an infinite loop. Though > such behavior has not been detected during regression testing and > bootstrapping on aarch64. > > gcc/ChangeLog: > > 2015-08-03 Andre Vieira <andre.simoesdiasvieira@arm.com> > > * match.pd: Added new patterns: > ((X {&,<<,>>} C0) {|,^} C1) {^,|} C2) > (X {|,^,&} C0) {<<,>>} C1 -> (X {<<,>>} C1) {|,^,&} (C0 {<<,>>} C1) > > gcc/testsuite/ChangeLog: > > 2015-08-03 Andre Vieira <andre.simoesdiasvieira@arm.com> > Hale Wang <hale.wang@arm.com> > > * gcc.dg/tree-ssa/forwprop-33.c: New test. > Ping.
On Thu, Sep 3, 2015 at 1:11 PM, Andre Vieira <Andre.SimoesDiasVieira@arm.com> wrote: > On 01/09/15 15:01, Richard Biener wrote: >> >> On Tue, Sep 1, 2015 at 3:40 PM, Andre Vieira >> <Andre.SimoesDiasVieira@arm.com> wrote: >>> >>> Hi Marc, >>> >>> On 28/08/15 19:07, Marc Glisse wrote: >>>> >>>> >>>> (not a review, I haven't even read the whole patch) >>>> >>>> On Fri, 28 Aug 2015, Andre Vieira wrote: >>>> >>>>> 2015-08-03 Andre Vieira <andre.simoesdiasvieira@arm.com> >>>>> >>>>> * match.pd: Added new patterns: >>>>> ((X {&,<<,>>} C0) {|,^} C1) {^,|} C2) >>>>> (X {|,^,&} C0) {<<,>>} C1 -> (X {<<,>>} C1) {|,^,&} (C0 {<<,>>} >>>>> C1) >>>> >>>> >>>> >>>> +(for op0 (rshift rshift lshift lshift bit_and bit_and) >>>> + op1 (bit_ior bit_xor bit_ior bit_xor bit_ior bit_xor) >>>> + op2 (bit_xor bit_ior bit_xor bit_ior bit_xor bit_ior) >>>> >>>> You can nest for-loops, it seems clearer as: >>>> (for op0 (rshift lshift bit_and) >>>> (for op1 (bit_ior bit_xor) >>>> op2 (bit_xor bit_ior) >>> >>> >>> >>> Will do, thank you for pointing it out. >>>> >>>> >>>> >>>> +(simplify >>>> + (op2:c >>>> + (op1:c >>>> + (op0 @0 INTEGER_CST@1) INTEGER_CST@2) INTEGER_CST@3) >>>> >>>> I suspect you will want more :s (single_use) and less :c >>>> (canonicalization >>>> should put constants in second position). >>>> >>> I can't find the definition of :s (single_use). >> >> >> Sorry for that - didn't get along updating it yet :/ It restricts >> matching to >> sub-expressions that have a single-use. So >> >> + a &= 0xd123; >> + unsigned short tem = a ^ 0x6040; >> + a = tem | 0xc031; /* Simplify _not_ to ((a & 0xd123) | 0xe071). */ >> ... use of tem ... >> >> we shouldn't do the simplifcation here because the expression >> (a & 0x123) ^ 0x6040 is kept live by 'tem'. >> >>> GCC internals do point out >>> that canonicalization does put constants in the second position, didnt >>> see >>> that first. Thank you for pointing it out. >>> >>>> + C1 = wi::bit_and_not (C1,C2); >>>> >>>> Space after ','. >>>> >>> Will do. >>> >>>> Having wide_int_storage in many places is surprising, I can't find >>>> similar >>>> code anywhere else in gcc. >>>> >>>> >>> >>> I tried looking for examples of something similar, I think I ended up >>> using >>> wide_int because I was able to convert easily to and from it and it has >>> the >>> "mask" and "wide_int_to_tree" functions. I welcome any suggestions on >>> what I >>> should be using here for integer constant transformations and >>> comparisons. >> >> >> Using wide-ints is fine, but you shouldn't need 'wide_int_storage' >> constructors - those >> are indeed odd. Is it just for the initializers of wide-ints? >> >> + wide_int zero_mask = wi::zero (prec); >> + wide_int C0 = wide_int_storage (@1); >> + wide_int C1 = wide_int_storage (@2); >> + wide_int C2 = wide_int_storage (@3); >> ... >> + zero_mask = wide_int_storage (wi::mask (C0.to_uhwi (), false, >> prec)); >> >> tree_to_uhwi (@1) should do the trick as well >> >> + C1 = wi::bit_and_not (C1,C2); >> + cst_emit = wi::bit_or (C1, C2); >> >> the ops should be replacable with @2 and @3, the store to C1 obviously not >> (but you can use a tree temporary and use wide_int_to_tree here to avoid >> the back-and-forth for the case where C1 is not assigned to). >> >> Note that transforms only doing association are prone to endless recursion >> in case some other pattern does the reverse op... >> >> Richard. >> >> >>> BR, >>> Andre >>> >> > Thank you for all the comments, see reworked version: > > Two new algorithmic optimisations: > 1.((X op0 C0) op1 C1) op2 C2) > with op0 = {&, >>, <<}, op1 = {|,^}, op2 = {|,^} and op1 != op2 > zero_mask has 1's for all bits that are sure to be 0 in (X op0 C0) > and 0's otherwise. > if (op1 == '^') C1 &= ~C2 (Only changed if actually emitted) > if ((C1 & ~zero_mask) == 0) then emit (X op0 C0) op2 (C1 op2 C2) > if ((C2 & ~zero_mask) == 0) then emit (X op0 C0) op1 (C1 op2 C2) > 2. (X {|,^,&} C0) {<<,>>} C1 -> (X {<<,>>} C1) {|,^,&} (C0 {<<,>>} C1) > > > This patch does two algorithmic optimisations that target patterns like: > (((x << 24) | 0x00FFFFFF) ^ 0xFF000000) and ((x ^ 0x40000002) >> 1) | > 0x80000000. > > The transformation uses the knowledge of which bits are zero after > operations like (X {&,<<,(unsigned)>>}) to combine constants, reducing > run-time operations. > The two examples above would be transformed into (X << 24) ^ 0xFFFFFFFF and > (X >> 1) ^ 0xa0000001 respectively. > > The second transformation enables more applications of the first. Also some > targets may benefit from delaying shift operations. I am aware that such an > optimization, in combination with one or more optimizations that cause the > reverse transformation, may lead to an infinite loop. Though such behavior > has not been detected during regression testing and bootstrapping on > aarch64. +/* (X bit_op C0) rshift C1 -> (X rshift C0) bit_op (C0 rshift C1) */ +(for bit_op (bit_ior bit_xor bit_and) +(simplify + (rshift (bit_op:s @0 INTEGER_CST@1) INTEGER_CST@2) + (bit_op + (rshift @0 @2) + { wide_int_to_tree (type, wi::rshift (@1, @2, TYPE_SIGN (type))); }))) + +/* (X bit_op C0) lshift C1 -> (X lshift C0) bit_op (C0 lshift C1) */ +(for bit_op (bit_ior bit_xor bit_and) +(simplify + (lshift (bit_op:s @0 INTEGER_CST@1) INTEGER_CST@2) + (bit_op + (lshift @0 @2) + { wide_int_to_tree (type, wi::lshift (@1, @2)); }))) this may be one case where not using wide-ints to be able to combine the patterns makes sense. Thus, (for shift (lshift rshift) (simplify (shift ...) (bit_op (shift @0 @2) (shift @1 @2)))) note that I'm worried we'd take on "invalid" ubsan here when the above applies to int foo (int i) { return (i & 0x7fffffff) >> 3; } int main () { return foo (0x80000007); } and i is negative. That's because right-shift of negative values invokes undefined behavior. IIRC in the middle-end we will not be taking advantage of that but the simplifications apply to GENERIC as well and thus may hit before ubsan instrumentation triggers(?) It would be nice if you could double-check that. + (if (!(op0 == RSHIFT_EXPR && !TYPE_UNSIGNED (type)) && wi::fits_uhwi_p (@1)) you only need fits_uhwi_p (@1) in the op0 != BIT_AND_EXPR case it seems, so better move it down to those cases. + (if (wi::eq_p (wi::bit_and (C1, zero_mask_not), wi::zero (prec))) I think you can write (if (wi::bit_and (...) == 0) or at least wi:eq_p (wi::bit_and (...), 0). I wonder if we shouldn't improve the pattern by handling (X op0 C0) transparently via using get_nonzero_bits (yeah, that's not exactly zero_mask but its inverse AFAIK). We'd wrap get_nonzero_bits in a helper that can handle GENERIC and your &, >>, << cases (hmm, such function must already exist somewhere...). So you'd reduce the pattern to + (for op1 (bit_ior bit_xor) + op2 (bit_xor bit_ior) +(simplify + (op2 + (op1:s @0 INTEGER_CST@2) INTEGER_CST@3)) (with { wide_int zero_mask_not = get_nonzero_bits (@0); ... } This would make use of value-range information determined by VRP for example. note that with your pattern you'd want to capture (op0:s @0 INTEGER_CST@1) like via (op0@4 @0 INTEGER_CST@1) so you can re-use it in the replacement like so: + (if (wi::eq_p (wi::bit_and (C1, zero_mask_not), wi::zero (prec))) + (op2 @4 { wide_int_to_tree (type, cst_emit); }) + (if (wi::eq_p (wi::bit_and (@3, zero_mask_not), wi::zero (prec))) + (op1 @4 { wide_int_to_tree (type, cst_emit); })))))))) the expression doesn't need a :s then obviously. Thanks and sorry for the delay in reviewing this. Richard. > gcc/ChangeLog: > > 2015-08-03 Andre Vieira <andre.simoesdiasvieira@arm.com> > > * match.pd: Added new patterns: > ((X {&,<<,>>} C0) {|,^} C1) {^,|} C2) > (X {|,^,&} C0) {<<,>>} C1 -> (X {<<,>>} C1) {|,^,&} (C0 {<<,>>} C1) > > gcc/testsuite/ChangeLog: > > 2015-08-03 Andre Vieira <andre.simoesdiasvieira@arm.com> > Hale Wang <hale.wang@arm.com> > > * gcc.dg/tree-ssa/forwprop-33.c: New test.
On 17/09/15 10:46, Richard Biener wrote: > On Thu, Sep 3, 2015 at 1:11 PM, Andre Vieira > <Andre.SimoesDiasVieira@arm.com> wrote: >> On 01/09/15 15:01, Richard Biener wrote: >>> >>> On Tue, Sep 1, 2015 at 3:40 PM, Andre Vieira >>> <Andre.SimoesDiasVieira@arm.com> wrote: >>>> >>>> Hi Marc, >>>> >>>> On 28/08/15 19:07, Marc Glisse wrote: >>>>> >>>>> >>>>> (not a review, I haven't even read the whole patch) >>>>> >>>>> On Fri, 28 Aug 2015, Andre Vieira wrote: >>>>> >>>>>> 2015-08-03 Andre Vieira <andre.simoesdiasvieira@arm.com> >>>>>> >>>>>> * match.pd: Added new patterns: >>>>>> ((X {&,<<,>>} C0) {|,^} C1) {^,|} C2) >>>>>> (X {|,^,&} C0) {<<,>>} C1 -> (X {<<,>>} C1) {|,^,&} (C0 {<<,>>} >>>>>> C1) >>>>> >>>>> >>>>> >>>>> +(for op0 (rshift rshift lshift lshift bit_and bit_and) >>>>> + op1 (bit_ior bit_xor bit_ior bit_xor bit_ior bit_xor) >>>>> + op2 (bit_xor bit_ior bit_xor bit_ior bit_xor bit_ior) >>>>> >>>>> You can nest for-loops, it seems clearer as: >>>>> (for op0 (rshift lshift bit_and) >>>>> (for op1 (bit_ior bit_xor) >>>>> op2 (bit_xor bit_ior) >>>> >>>> >>>> >>>> Will do, thank you for pointing it out. >>>>> >>>>> >>>>> >>>>> +(simplify >>>>> + (op2:c >>>>> + (op1:c >>>>> + (op0 @0 INTEGER_CST@1) INTEGER_CST@2) INTEGER_CST@3) >>>>> >>>>> I suspect you will want more :s (single_use) and less :c >>>>> (canonicalization >>>>> should put constants in second position). >>>>> >>>> I can't find the definition of :s (single_use). >>> >>> >>> Sorry for that - didn't get along updating it yet :/ It restricts >>> matching to >>> sub-expressions that have a single-use. So >>> >>> + a &= 0xd123; >>> + unsigned short tem = a ^ 0x6040; >>> + a = tem | 0xc031; /* Simplify _not_ to ((a & 0xd123) | 0xe071). */ >>> ... use of tem ... >>> >>> we shouldn't do the simplifcation here because the expression >>> (a & 0x123) ^ 0x6040 is kept live by 'tem'. >>> >>>> GCC internals do point out >>>> that canonicalization does put constants in the second position, didnt >>>> see >>>> that first. Thank you for pointing it out. >>>> >>>>> + C1 = wi::bit_and_not (C1,C2); >>>>> >>>>> Space after ','. >>>>> >>>> Will do. >>>> >>>>> Having wide_int_storage in many places is surprising, I can't find >>>>> similar >>>>> code anywhere else in gcc. >>>>> >>>>> >>>> >>>> I tried looking for examples of something similar, I think I ended up >>>> using >>>> wide_int because I was able to convert easily to and from it and it has >>>> the >>>> "mask" and "wide_int_to_tree" functions. I welcome any suggestions on >>>> what I >>>> should be using here for integer constant transformations and >>>> comparisons. >>> >>> >>> Using wide-ints is fine, but you shouldn't need 'wide_int_storage' >>> constructors - those >>> are indeed odd. Is it just for the initializers of wide-ints? >>> >>> + wide_int zero_mask = wi::zero (prec); >>> + wide_int C0 = wide_int_storage (@1); >>> + wide_int C1 = wide_int_storage (@2); >>> + wide_int C2 = wide_int_storage (@3); >>> ... >>> + zero_mask = wide_int_storage (wi::mask (C0.to_uhwi (), false, >>> prec)); >>> >>> tree_to_uhwi (@1) should do the trick as well >>> >>> + C1 = wi::bit_and_not (C1,C2); >>> + cst_emit = wi::bit_or (C1, C2); >>> >>> the ops should be replacable with @2 and @3, the store to C1 obviously not >>> (but you can use a tree temporary and use wide_int_to_tree here to avoid >>> the back-and-forth for the case where C1 is not assigned to). >>> >>> Note that transforms only doing association are prone to endless recursion >>> in case some other pattern does the reverse op... >>> >>> Richard. >>> >>> >>>> BR, >>>> Andre >>>> >>> >> Thank you for all the comments, see reworked version: >> >> Two new algorithmic optimisations: >> 1.((X op0 C0) op1 C1) op2 C2) >> with op0 = {&, >>, <<}, op1 = {|,^}, op2 = {|,^} and op1 != op2 >> zero_mask has 1's for all bits that are sure to be 0 in (X op0 C0) >> and 0's otherwise. >> if (op1 == '^') C1 &= ~C2 (Only changed if actually emitted) >> if ((C1 & ~zero_mask) == 0) then emit (X op0 C0) op2 (C1 op2 C2) >> if ((C2 & ~zero_mask) == 0) then emit (X op0 C0) op1 (C1 op2 C2) >> 2. (X {|,^,&} C0) {<<,>>} C1 -> (X {<<,>>} C1) {|,^,&} (C0 {<<,>>} C1) >> >> >> This patch does two algorithmic optimisations that target patterns like: >> (((x << 24) | 0x00FFFFFF) ^ 0xFF000000) and ((x ^ 0x40000002) >> 1) | >> 0x80000000. >> >> The transformation uses the knowledge of which bits are zero after >> operations like (X {&,<<,(unsigned)>>}) to combine constants, reducing >> run-time operations. >> The two examples above would be transformed into (X << 24) ^ 0xFFFFFFFF and >> (X >> 1) ^ 0xa0000001 respectively. >> >> The second transformation enables more applications of the first. Also some >> targets may benefit from delaying shift operations. I am aware that such an >> optimization, in combination with one or more optimizations that cause the >> reverse transformation, may lead to an infinite loop. Though such behavior >> has not been detected during regression testing and bootstrapping on >> aarch64. > > +/* (X bit_op C0) rshift C1 -> (X rshift C0) bit_op (C0 rshift C1) */ > +(for bit_op (bit_ior bit_xor bit_and) > +(simplify > + (rshift (bit_op:s @0 INTEGER_CST@1) INTEGER_CST@2) > + (bit_op > + (rshift @0 @2) > + { wide_int_to_tree (type, wi::rshift (@1, @2, TYPE_SIGN (type))); }))) > + > +/* (X bit_op C0) lshift C1 -> (X lshift C0) bit_op (C0 lshift C1) */ > +(for bit_op (bit_ior bit_xor bit_and) > +(simplify > + (lshift (bit_op:s @0 INTEGER_CST@1) INTEGER_CST@2) > + (bit_op > + (lshift @0 @2) > + { wide_int_to_tree (type, wi::lshift (@1, @2)); }))) Will do, good to see that my second transformation still picks up the shift @1 @2 as a constant. I'm assuming there is some constant folding going on between simplify transformations? > > this may be one case where not using wide-ints to be able to combine the > patterns makes sense. Thus, > > (for shift (lshift rshift) > (simplify > (shift ...) > (bit_op > (shift @0 @2) > (shift @1 @2)))) > > note that I'm worried we'd take on "invalid" ubsan here when the above > applies to > > int foo (int i) > { > return (i & 0x7fffffff) >> 3; > } > int main () { return foo (0x80000007); } > > and i is negative. That's because right-shift of negative values > invokes undefined > behavior. IIRC in the middle-end we will not be taking advantage of > that but the > simplifications apply to GENERIC as well and thus may hit before ubsan > instrumentation triggers(?) It would be nice if you could double-check that. I was looking into this and I understand your worries, though, I found out that for the particular case of shifts and bit_and there already is a simplify transformation that does the same, regardless of the sign. /* Fold (X & C2) << C1 into (X << C1) & (C2 << C1) (X & C2) >> C1 into (X >> C1) & (C2 >> C1). */ (for shift (lshift rshift) (simplify (shift (convert?:s (bit_and:s @0 INTEGER_CST@2)) INTEGER_CST@1) (if (tree_nop_conversion_p (type, TREE_TYPE (@0))) (with { tree mask = int_const_binop (shift, fold_convert (type, @2), @1); } (bit_and (shift (convert @0) @1) { mask; }))))) Now, I don't quite understand what you mean by ubsan instrumentation, will GCC introduce guards into code where it detects potential undefined behavior? Also, it might be worth to note that right shift of negative values is denoted as "implementation defined" by the C standard. GCC however doesn't include it in its list of implementation defined behavior so I guess that is why you refer to it as undefined? Should we perhaps disable transformations where we can not guarantee that the right shift produced is not one of negative values? I.e. prohibit this transformation for: 1) signed types and op1 == bit_xor 2) signed types and op1 == bit_and and C1 has sign bit set. Also would it be useful in cases where you have signed shift and bit_and, and C1 is not negative, to do the transformation but replace the signed shift by an unsigned shift. This to make sure we don't introduce undefined/implementation defined behavior were there was none. This does however change the current behavior! > > + (if (!(op0 == RSHIFT_EXPR && !TYPE_UNSIGNED (type)) && wi::fits_uhwi_p (@1)) > > you only need fits_uhwi_p (@1) in the op0 != BIT_AND_EXPR case it > seems, so better > move it down to those cases. So I used to, but I had the problem that I didn't know how to make it "fail" the matching if this was not the case. For instance if op0 is a lshift for which the constant doesn't fit uhwi, then it would fall through and never set the zero mask, potentially leading to a wrong transformation. Now I'm not sure this can happen, since that would mean that either constant @2 or @3 need to be all 1's and that might already be caught by some other transformation, but its wrong to rely on such behavior IMO. So for now I have changed it to: (simplify (op2 (op1:s (op0@4 @0 INTEGER_CST@1) INTEGER_CST@2) INTEGER_CST@3) (if (!(op0 == RSHIFT_EXPR && !TYPE_UNSIGNED (type)) && (op0 == BIT_AND_EXPR || wi::fits_uhwi_p (@1))) It would be cool to have a FAIL expression, usable in the with clauses, to make the pattern match fail a bit like the one in the machine description language. > > + (if (wi::eq_p (wi::bit_and (C1, zero_mask_not), wi::zero (prec))) > > I think you can write > > (if (wi::bit_and (...) == 0) > > or at least wi:eq_p (wi::bit_and (...), 0). > wi::bit_and (...) == 0 seems to be doing the trick. > I wonder if we shouldn't improve the pattern by handling (X op0 C0) > transparently > via using get_nonzero_bits (yeah, that's not exactly zero_mask but its > inverse AFAIK). > We'd wrap get_nonzero_bits in a helper that can handle GENERIC and your > &, >>, << cases (hmm, such function must already exist somewhere...). So you'd > reduce the pattern to > > + (for op1 (bit_ior bit_xor) > + op2 (bit_xor bit_ior) > +(simplify > + (op2 > + (op1:s @0 INTEGER_CST@2) INTEGER_CST@3)) > (with > { > wide_int zero_mask_not = get_nonzero_bits (@0); > ... > } > > This would make use of value-range information determined by VRP for example. I'll go look for such a function. > > note that with your pattern you'd want to capture (op0:s @0 INTEGER_CST@1) > like via (op0@4 @0 INTEGER_CST@1) so you can re-use it in the replacement > like so: > > + (if (wi::eq_p (wi::bit_and (C1, zero_mask_not), wi::zero (prec))) > + (op2 @4 { wide_int_to_tree (type, cst_emit); }) > + (if (wi::eq_p (wi::bit_and (@3, zero_mask_not), wi::zero (prec))) > + (op1 @4 { wide_int_to_tree (type, cst_emit); })))))))) > > the expression doesn't need a :s then obviously. Yeah makes sense. > > Thanks and sorry for the delay in reviewing this. > Richard. > Thank you for all the comments! > >> gcc/ChangeLog: >> >> 2015-08-03 Andre Vieira <andre.simoesdiasvieira@arm.com> >> >> * match.pd: Added new patterns: >> ((X {&,<<,>>} C0) {|,^} C1) {^,|} C2) >> (X {|,^,&} C0) {<<,>>} C1 -> (X {<<,>>} C1) {|,^,&} (C0 {<<,>>} C1) >> >> gcc/testsuite/ChangeLog: >> >> 2015-08-03 Andre Vieira <andre.simoesdiasvieira@arm.com> >> Hale Wang <hale.wang@arm.com> >> >> * gcc.dg/tree-ssa/forwprop-33.c: New test. >
On Fri, Sep 25, 2015 at 1:30 PM, Andre Vieira <Andre.SimoesDiasVieira@arm.com> wrote: > On 17/09/15 10:46, Richard Biener wrote: >> >> On Thu, Sep 3, 2015 at 1:11 PM, Andre Vieira >> <Andre.SimoesDiasVieira@arm.com> wrote: >>> >>> On 01/09/15 15:01, Richard Biener wrote: >>>> >>>> >>>> On Tue, Sep 1, 2015 at 3:40 PM, Andre Vieira >>>> <Andre.SimoesDiasVieira@arm.com> wrote: >>>>> >>>>> >>>>> Hi Marc, >>>>> >>>>> On 28/08/15 19:07, Marc Glisse wrote: >>>>>> >>>>>> >>>>>> >>>>>> (not a review, I haven't even read the whole patch) >>>>>> >>>>>> On Fri, 28 Aug 2015, Andre Vieira wrote: >>>>>> >>>>>>> 2015-08-03 Andre Vieira <andre.simoesdiasvieira@arm.com> >>>>>>> >>>>>>> * match.pd: Added new patterns: >>>>>>> ((X {&,<<,>>} C0) {|,^} C1) {^,|} C2) >>>>>>> (X {|,^,&} C0) {<<,>>} C1 -> (X {<<,>>} C1) {|,^,&} (C0 {<<,>>} >>>>>>> C1) >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> +(for op0 (rshift rshift lshift lshift bit_and bit_and) >>>>>> + op1 (bit_ior bit_xor bit_ior bit_xor bit_ior bit_xor) >>>>>> + op2 (bit_xor bit_ior bit_xor bit_ior bit_xor bit_ior) >>>>>> >>>>>> You can nest for-loops, it seems clearer as: >>>>>> (for op0 (rshift lshift bit_and) >>>>>> (for op1 (bit_ior bit_xor) >>>>>> op2 (bit_xor bit_ior) >>>>> >>>>> >>>>> >>>>> >>>>> Will do, thank you for pointing it out. >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> +(simplify >>>>>> + (op2:c >>>>>> + (op1:c >>>>>> + (op0 @0 INTEGER_CST@1) INTEGER_CST@2) INTEGER_CST@3) >>>>>> >>>>>> I suspect you will want more :s (single_use) and less :c >>>>>> (canonicalization >>>>>> should put constants in second position). >>>>>> >>>>> I can't find the definition of :s (single_use). >>>> >>>> >>>> >>>> Sorry for that - didn't get along updating it yet :/ It restricts >>>> matching to >>>> sub-expressions that have a single-use. So >>>> >>>> + a &= 0xd123; >>>> + unsigned short tem = a ^ 0x6040; >>>> + a = tem | 0xc031; /* Simplify _not_ to ((a & 0xd123) | 0xe071). */ >>>> ... use of tem ... >>>> >>>> we shouldn't do the simplifcation here because the expression >>>> (a & 0x123) ^ 0x6040 is kept live by 'tem'. >>>> >>>>> GCC internals do point out >>>>> that canonicalization does put constants in the second position, didnt >>>>> see >>>>> that first. Thank you for pointing it out. >>>>> >>>>>> + C1 = wi::bit_and_not (C1,C2); >>>>>> >>>>>> Space after ','. >>>>>> >>>>> Will do. >>>>> >>>>>> Having wide_int_storage in many places is surprising, I can't find >>>>>> similar >>>>>> code anywhere else in gcc. >>>>>> >>>>>> >>>>> >>>>> I tried looking for examples of something similar, I think I ended up >>>>> using >>>>> wide_int because I was able to convert easily to and from it and it has >>>>> the >>>>> "mask" and "wide_int_to_tree" functions. I welcome any suggestions on >>>>> what I >>>>> should be using here for integer constant transformations and >>>>> comparisons. >>>> >>>> >>>> >>>> Using wide-ints is fine, but you shouldn't need 'wide_int_storage' >>>> constructors - those >>>> are indeed odd. Is it just for the initializers of wide-ints? >>>> >>>> + wide_int zero_mask = wi::zero (prec); >>>> + wide_int C0 = wide_int_storage (@1); >>>> + wide_int C1 = wide_int_storage (@2); >>>> + wide_int C2 = wide_int_storage (@3); >>>> ... >>>> + zero_mask = wide_int_storage (wi::mask (C0.to_uhwi (), false, >>>> prec)); >>>> >>>> tree_to_uhwi (@1) should do the trick as well >>>> >>>> + C1 = wi::bit_and_not (C1,C2); >>>> + cst_emit = wi::bit_or (C1, C2); >>>> >>>> the ops should be replacable with @2 and @3, the store to C1 obviously >>>> not >>>> (but you can use a tree temporary and use wide_int_to_tree here to avoid >>>> the back-and-forth for the case where C1 is not assigned to). >>>> >>>> Note that transforms only doing association are prone to endless >>>> recursion >>>> in case some other pattern does the reverse op... >>>> >>>> Richard. >>>> >>>> >>>>> BR, >>>>> Andre >>>>> >>>> >>> Thank you for all the comments, see reworked version: >>> >>> Two new algorithmic optimisations: >>> 1.((X op0 C0) op1 C1) op2 C2) >>> with op0 = {&, >>, <<}, op1 = {|,^}, op2 = {|,^} and op1 != op2 >>> zero_mask has 1's for all bits that are sure to be 0 in (X op0 C0) >>> and 0's otherwise. >>> if (op1 == '^') C1 &= ~C2 (Only changed if actually emitted) >>> if ((C1 & ~zero_mask) == 0) then emit (X op0 C0) op2 (C1 op2 C2) >>> if ((C2 & ~zero_mask) == 0) then emit (X op0 C0) op1 (C1 op2 C2) >>> 2. (X {|,^,&} C0) {<<,>>} C1 -> (X {<<,>>} C1) {|,^,&} (C0 {<<,>>} C1) >>> >>> >>> This patch does two algorithmic optimisations that target patterns like: >>> (((x << 24) | 0x00FFFFFF) ^ 0xFF000000) and ((x ^ 0x40000002) >> 1) | >>> 0x80000000. >>> >>> The transformation uses the knowledge of which bits are zero after >>> operations like (X {&,<<,(unsigned)>>}) to combine constants, reducing >>> run-time operations. >>> The two examples above would be transformed into (X << 24) ^ 0xFFFFFFFF >>> and >>> (X >> 1) ^ 0xa0000001 respectively. >>> >>> The second transformation enables more applications of the first. Also >>> some >>> targets may benefit from delaying shift operations. I am aware that such >>> an >>> optimization, in combination with one or more optimizations that cause >>> the >>> reverse transformation, may lead to an infinite loop. Though such >>> behavior >>> has not been detected during regression testing and bootstrapping on >>> aarch64. >> >> >> +/* (X bit_op C0) rshift C1 -> (X rshift C0) bit_op (C0 rshift C1) */ >> +(for bit_op (bit_ior bit_xor bit_and) >> +(simplify >> + (rshift (bit_op:s @0 INTEGER_CST@1) INTEGER_CST@2) >> + (bit_op >> + (rshift @0 @2) >> + { wide_int_to_tree (type, wi::rshift (@1, @2, TYPE_SIGN (type))); }))) >> + >> +/* (X bit_op C0) lshift C1 -> (X lshift C0) bit_op (C0 lshift C1) */ >> +(for bit_op (bit_ior bit_xor bit_and) >> +(simplify >> + (lshift (bit_op:s @0 INTEGER_CST@1) INTEGER_CST@2) >> + (bit_op >> + (lshift @0 @2) >> + { wide_int_to_tree (type, wi::lshift (@1, @2)); }))) > > > Will do, good to see that my second transformation still picks up the shift > @1 @2 as a constant. I'm assuming there is some constant folding going on > between simplify transformations? Yes. >> >> this may be one case where not using wide-ints to be able to combine the >> patterns makes sense. Thus, >> >> (for shift (lshift rshift) >> (simplify >> (shift ...) >> (bit_op >> (shift @0 @2) >> (shift @1 @2)))) >> >> note that I'm worried we'd take on "invalid" ubsan here when the above >> applies to >> >> int foo (int i) >> { >> return (i & 0x7fffffff) >> 3; >> } >> int main () { return foo (0x80000007); } >> >> and i is negative. That's because right-shift of negative values >> invokes undefined >> behavior. IIRC in the middle-end we will not be taking advantage of >> that but the >> simplifications apply to GENERIC as well and thus may hit before ubsan >> instrumentation triggers(?) It would be nice if you could double-check >> that. > > > I was looking into this and I understand your worries, though, I found out > that for the particular case of shifts and bit_and there already is a > simplify transformation that does the same, regardless of the sign. > > /* Fold (X & C2) << C1 into (X << C1) & (C2 << C1) > (X & C2) >> C1 into (X >> C1) & (C2 >> C1). */ > (for shift (lshift rshift) > (simplify > (shift (convert?:s (bit_and:s @0 INTEGER_CST@2)) INTEGER_CST@1) > (if (tree_nop_conversion_p (type, TREE_TYPE (@0))) > (with { tree mask = int_const_binop (shift, fold_convert (type, @2), @1); > } > (bit_and (shift (convert @0) @1) { mask; }))))) I see ... also an opportunity to merge this pattern with yours. > Now, I don't quite understand what you mean by ubsan instrumentation, will > GCC introduce guards into code where it detects potential undefined > behavior? Yes. > Also, it might be worth to note that right shift of negative > values is denoted as "implementation defined" by the C standard. GCC however > doesn't include it in its list of implementation defined behavior so I guess > that is why you refer to it as undefined? Not sure, I thought it was undefined. If its implementation defined then GCC needs to document its behavior. > Should we perhaps disable transformations where we can not guarantee that > the right shift produced is not one of negative values? I.e. prohibit this > transformation for: > 1) signed types and op1 == bit_xor > 2) signed types and op1 == bit_and and C1 has sign bit set. > > Also would it be useful in cases where you have signed shift and bit_and, > and C1 is not negative, to do the transformation but replace the signed > shift by an unsigned shift. This to make sure we don't introduce > undefined/implementation defined behavior were there was none. > > This does however change the current behavior! Yeah, so unless somebody else chimes in let's consider this as followup only. >> >> + (if (!(op0 == RSHIFT_EXPR && !TYPE_UNSIGNED (type)) && wi::fits_uhwi_p >> (@1)) >> >> you only need fits_uhwi_p (@1) in the op0 != BIT_AND_EXPR case it >> seems, so better >> move it down to those cases. > > > So I used to, but I had the problem that I didn't know how to make it "fail" > the matching if this was not the case. For instance if op0 is a lshift for > which the constant doesn't fit uhwi, then it would fall through and never > set the zero mask, potentially leading to a wrong transformation. Now I'm > not sure this can happen, since that would mean that either constant @2 or > @3 need to be all 1's and that might already be caught by some other > transformation, but its wrong to rely on such behavior IMO. So for now I > have changed it to: > > (simplify > (op2 > (op1:s > (op0@4 @0 INTEGER_CST@1) INTEGER_CST@2) INTEGER_CST@3) > (if (!(op0 == RSHIFT_EXPR && !TYPE_UNSIGNED (type)) && > (op0 == BIT_AND_EXPR || wi::fits_uhwi_p (@1))) > > > It would be cool to have a FAIL expression, usable in the with clauses, to > make the pattern match fail a bit like the one in the machine description > language. I'll think about it. Currently you'd need to add a 'bool fail' in the with and initialize it, adding a (if (!fail) ...) after it. >> >> + (if (wi::eq_p (wi::bit_and (C1, zero_mask_not), wi::zero (prec))) >> >> I think you can write >> >> (if (wi::bit_and (...) == 0) >> >> or at least wi:eq_p (wi::bit_and (...), 0). >> > > wi::bit_and (...) == 0 seems to be doing the trick. > >> I wonder if we shouldn't improve the pattern by handling (X op0 C0) >> transparently >> via using get_nonzero_bits (yeah, that's not exactly zero_mask but its >> inverse AFAIK). >> We'd wrap get_nonzero_bits in a helper that can handle GENERIC and your >> &, >>, << cases (hmm, such function must already exist somewhere...). So >> you'd >> reduce the pattern to >> >> + (for op1 (bit_ior bit_xor) >> + op2 (bit_xor bit_ior) >> +(simplify >> + (op2 >> + (op1:s @0 INTEGER_CST@2) INTEGER_CST@3)) >> (with >> { >> wide_int zero_mask_not = get_nonzero_bits (@0); >> ... >> } >> >> This would make use of value-range information determined by VRP for >> example. > > > I'll go look for such a function. > >> >> note that with your pattern you'd want to capture (op0:s @0 INTEGER_CST@1) >> like via (op0@4 @0 INTEGER_CST@1) so you can re-use it in the replacement >> like so: >> >> + (if (wi::eq_p (wi::bit_and (C1, zero_mask_not), wi::zero (prec))) >> + (op2 @4 { wide_int_to_tree (type, cst_emit); }) >> + (if (wi::eq_p (wi::bit_and (@3, zero_mask_not), wi::zero (prec))) >> + (op1 @4 { wide_int_to_tree (type, cst_emit); })))))))) >> >> the expression doesn't need a :s then obviously. > > > Yeah makes sense. >> >> >> Thanks and sorry for the delay in reviewing this. >> Richard. >> > > Thank you for all the comments! No problem! >> >>> gcc/ChangeLog: >>> >>> 2015-08-03 Andre Vieira <andre.simoesdiasvieira@arm.com> >>> >>> * match.pd: Added new patterns: >>> ((X {&,<<,>>} C0) {|,^} C1) {^,|} C2) >>> (X {|,^,&} C0) {<<,>>} C1 -> (X {<<,>>} C1) {|,^,&} (C0 {<<,>>} C1) >>> >>> gcc/testsuite/ChangeLog: >>> >>> 2015-08-03 Andre Vieira <andre.simoesdiasvieira@arm.com> >>> Hale Wang <hale.wang@arm.com> >>> >>> * gcc.dg/tree-ssa/forwprop-33.c: New test. >> >> >
From 3d1d4d838fed9af45aea9fa99f8954585fee7c23 Mon Sep 17 00:00:00 2001 From: Andre Simoes Dias Vieira <andsim01@arm.com> Date: Wed, 2 Sep 2015 16:47:38 +0100 Subject: [PATCH] algorithmic optimization v2 --- gcc/match.pd | 70 +++++++++++++++++++++++++++++ gcc/testsuite/gcc.dg/tree-ssa/forwprop-33.c | 42 +++++++++++++++++ 2 files changed, 112 insertions(+) create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/forwprop-33.c diff --git a/gcc/match.pd b/gcc/match.pd index fb4b342d31d26a03bc756c538f6635f2acf6ddb2..6138591c0cef1814dcbd6313dedaa95a91700dc2 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -710,6 +710,76 @@ along with GCC; see the file COPYING3. If not see && tree_nop_conversion_p (type, TREE_TYPE (@1))) (convert (bit_and (bit_not @1) @0)))) +/* (X bit_op C0) rshift C1 -> (X rshift C0) bit_op (C0 rshift C1) */ +(for bit_op (bit_ior bit_xor bit_and) +(simplify + (rshift (bit_op:s @0 INTEGER_CST@1) INTEGER_CST@2) + (bit_op + (rshift @0 @2) + { wide_int_to_tree (type, wi::rshift (@1, @2, TYPE_SIGN (type))); }))) + +/* (X bit_op C0) lshift C1 -> (X lshift C0) bit_op (C0 lshift C1) */ +(for bit_op (bit_ior bit_xor bit_and) +(simplify + (lshift (bit_op:s @0 INTEGER_CST@1) INTEGER_CST@2) + (bit_op + (lshift @0 @2) + { wide_int_to_tree (type, wi::lshift (@1, @2)); }))) + + +/* ((X op0 C0) op1 C1) op2 C2) + with op0 = {&, >>, <<}, op1 = {|,^}, op2 = {|,^} and op1 != op2 + zero_mask has 1's for all bits that are sure to be 0 in (X op0 C0) + and 0's otherwise. + if (op1 == '^') C1 &= ~C2; + if ((C1 & ~zero_mask) == 0) then emit (X op0 C0) op2 (C1 op2 C2) + if ((C2 & ~zero_mask) == 0) then emit (X op0 C0) op1 (C1 op2 C2) +*/ +(for op0 (rshift lshift bit_and) + (for op1 (bit_ior bit_xor) + op2 (bit_xor bit_ior) +(simplify + (op2 + (op1:s + (op0:s @0 INTEGER_CST@1) INTEGER_CST@2) INTEGER_CST@3) + (if (!(op0 == RSHIFT_EXPR && !TYPE_UNSIGNED (type)) && wi::fits_uhwi_p (@1)) + (with + { + unsigned int prec = TYPE_PRECISION (type); + wide_int zero_mask_not; + wide_int C1; + wide_int cst_emit; + if (op0 == BIT_AND_EXPR) + { + zero_mask_not = @1; + } + else if (op0 == LSHIFT_EXPR) + { + zero_mask_not = wi::bit_not (wi::mask (tree_to_uhwi (@1), false, + prec)); + } + else if (op0 == RSHIFT_EXPR) + { + unsigned HOST_WIDE_INT m = prec - tree_to_uhwi (@1); + zero_mask_not = wi::bit_not (wi::mask (m, true, prec)); + } + + if (op1 == BIT_XOR_EXPR) + { + C1 = wi::bit_and_not (@2, @3); + cst_emit = wi::bit_or (C1, @3); + } + else + { + C1 = @2; + cst_emit = wi::bit_xor (@2, @3); + } + } + (if (wi::eq_p (wi::bit_and (C1, zero_mask_not), wi::zero (prec))) + (op2 (op0 @0 @1) { wide_int_to_tree (type, cst_emit); }) + (if (wi::eq_p (wi::bit_and (@3, zero_mask_not), wi::zero (prec))) + (op1 (op0 @0 @1) { wide_int_to_tree (type, cst_emit); })))))))) + /* Associate (p +p off1) +p off2 as (p +p (off1 + off2)). */ (simplify (pointer_plus (pointer_plus:s @0 @1) @3) diff --git a/gcc/testsuite/gcc.dg/tree-ssa/forwprop-33.c b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-33.c new file mode 100644 index 0000000000000000000000000000000000000000..c8940d62a7a9370e9d2b911badfc6d085f988304 --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/forwprop-33.c @@ -0,0 +1,42 @@ +/* { dg-do compile } */ +/* { dg-options "-O -fdump-tree-forwprop1" } */ + +unsigned short +foo (unsigned short a) +{ + a ^= 0x4002; + a >>= 1; + a |= 0x8000; /* Simplify to ((a >> 1) ^ 0xa001). */ + return a; +} +/* { dg-final { scan-tree-dump "\\^ 40961" "forwprop1" } } */ + +unsigned short +bar (unsigned short a) +{ + a |= 0x4002; + a <<= 1; + a ^= 0x0001; /* Simplify to ((a << 1) | 0x8005). */ + return a; +} +/* { dg-final { scan-tree-dump "\\| 32773" "forwprop1" } } */ + +unsigned short +baz (unsigned short a) +{ + a &= 0xd123; + a ^= 0x6040; + a |= 0xc031; /* Simplify to ((a & 0xd123) | 0xe071). */ + return a; +} +/* { dg-final { scan-tree-dump "\\| 57457" "forwprop1" } } */ + +short +qux (short a) +{ + a ^= 0x8002; + a >>= 1; + a |= 0x8000; /* Only move shift inward: (((a >> 1) ^ 0x4001 |) 0x8000). */ + return a; +} +/* { dg-final { scan-tree-dump "\\^ -16383" "forwprop1" } } */ -- 1.9.1