| Message ID | ri6h740a7ap.fsf@suse.cz |
|---|---|
| State | New |
| Headers | show |
| Series | tree-sra: Fix union handling in build_reconstructed_reference (PR 105860) | expand |
On Fri, 1 Jul 2022, Martin Jambor wrote: > Hi, > > As the testcase in PR 105860 shows, the code that tries to re-use the > handled_component chains in SRA can be horribly confused by unions, > where it thinks it has found a compatible structure under which it can > chain the references, but in fact it found the type it was looking > for elsewhere in a union and generated a write to a completely wrong > part of an aggregate. > > I don't remember whether the plan was to support unions at all in > build_reconstructed_reference but it can work, to an extent, if we > make sure that we start the search only outside the outermost union, > which is what the patch does (and the extra testcase verifies). > > Bootstrapped and tested on x86_64-linux. OK for trunk and then for > release branches? OK, but I'm wondering if the same problem can arise when the handled_component_p includes VIEW_CONVERTs or BIT_FIELD_REFs both of which may pun to a type already seen in a more inner referece. Thus, is the actual problem that build_reconstructed_reference searches for the outermost match of the type rather than the innermost match? So should it search inner-to-outer instead (or for the last match in the current way of searching?) Thanks, Richard. > Thanks, > > Martin > > > gcc/ChangeLog: > > 2022-07-01 Martin Jambor <mjambor@suse.cz> > > PR tree-optimization/105860 > * tree-sra.cc (build_reconstructed_reference): Start expr > traversal only just below the outermost union. > > gcc/testsuite/ChangeLog: > > 2022-07-01 Martin Jambor <mjambor@suse.cz> > > PR tree-optimization/105860 > * gcc.dg/tree-ssa/alias-access-path-13.c: New test. > * gcc.dg/tree-ssa/pr105860.c: Likewise. > --- > .../gcc.dg/tree-ssa/alias-access-path-13.c | 31 +++++++++ > gcc/testsuite/gcc.dg/tree-ssa/pr105860.c | 63 +++++++++++++++++++ > gcc/tree-sra.cc | 13 +++- > 3 files changed, 106 insertions(+), 1 deletion(-) > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c > create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr105860.c > > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c b/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c > new file mode 100644 > index 00000000000..e502a97bc75 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c > @@ -0,0 +1,31 @@ > +/* { dg-do compile } */ > +/* { dg-options "-O2 -fdump-tree-fre1" } */ > + > +struct inn > +{ > + int val; > +}; > + > +union foo > +{ > + struct inn inn; > + long int baz; > +} *fooptr; > + > +struct bar > +{ > + union foo foo; > + int val2; > +} *barptr; > + > +int > +test () > +{ > + union foo foo; > + foo.inn.val = 0; > + barptr->val2 = 123; > + *fooptr = foo; > + return barptr->val2; > +} > + > +/* { dg-final { scan-tree-dump-times "return 123" 1 "fre1"} } */ > diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c b/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c > new file mode 100644 > index 00000000000..77bcb4a6739 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c > @@ -0,0 +1,63 @@ > +/* { dg-do run } */ > +/* { dg-options "-O1" } */ > + > +struct S1 { > + unsigned int _0; > + unsigned int _1; > +} ; > +struct S2 { > + struct S1 _s1; > + unsigned long _x2; > +} ; > + > +struct ufld_type1 { > + unsigned int _u1t; > + struct S2 _s2; > +} ; > + > +struct ufld_type2 { > + unsigned int _u2t; > + struct S1 _s1; > +} ; > +struct parm_type { > + union { > + struct ufld_type1 var_1; > + struct ufld_type2 var_2; > + } U; > +}; > + > +struct parm_type bad_function( struct parm_type arg0 ) > +{ > + struct parm_type rv; > + struct S2 var4; > + switch( arg0.U.var_2._u2t ) { > + case 4294967041: > + var4._s1 = arg0.U.var_1._s2._s1; > + rv.U.var_1._u1t = 4294967041; > + rv.U.var_1._s2 = var4; > + break; > + case 4294967043: > + rv.U.var_2._u2t = 4294967043; > + rv.U.var_2._s1 = arg0.U.var_2._s1; > + break; > + default: > + break; > + } > + return rv; > +} > + > +int main() { > + struct parm_type val; > + struct parm_type out; > + val.U.var_2._u2t = 4294967043; > + val.U.var_2._s1._0 = 0x01010101; > + val.U.var_2._s1._1 = 0x02020202; > + out = bad_function(val); > + if (val.U.var_2._u2t != 4294967043) > + __builtin_abort (); > + if (out.U.var_2._s1._0 != 0x01010101) > + __builtin_abort (); > + if (val.U.var_2._s1._1 != 0x02020202 ) > + __builtin_abort (); > + return 0; > +} > diff --git a/gcc/tree-sra.cc b/gcc/tree-sra.cc > index 081c51b58a4..099e8dbe873 100644 > --- a/gcc/tree-sra.cc > +++ b/gcc/tree-sra.cc > @@ -1667,7 +1667,18 @@ build_ref_for_offset (location_t loc, tree base, poly_int64 offset, > static tree > build_reconstructed_reference (location_t, tree base, struct access *model) > { > - tree expr = model->expr, prev_expr = NULL; > + tree expr = model->expr; > + /* We have to make sure to start just below the outermost union. */ > + tree start_expr = expr; > + while (handled_component_p (expr)) > + { > + if (TREE_CODE (TREE_TYPE (TREE_OPERAND (expr, 0))) == UNION_TYPE) > + start_expr = expr; > + expr = TREE_OPERAND (expr, 0); > + } > + > + expr = start_expr; > + tree prev_expr = NULL_TREE; > while (!types_compatible_p (TREE_TYPE (expr), TREE_TYPE (base))) > { > if (!handled_component_p (expr)) >
Hi, On Mon, Jul 04 2022, Richard Biener wrote: > On Fri, 1 Jul 2022, Martin Jambor wrote: > >> Hi, >> >> As the testcase in PR 105860 shows, the code that tries to re-use the >> handled_component chains in SRA can be horribly confused by unions, >> where it thinks it has found a compatible structure under which it can >> chain the references, but in fact it found the type it was looking >> for elsewhere in a union and generated a write to a completely wrong >> part of an aggregate. >> >> I don't remember whether the plan was to support unions at all in >> build_reconstructed_reference but it can work, to an extent, if we >> make sure that we start the search only outside the outermost union, >> which is what the patch does (and the extra testcase verifies). >> >> Bootstrapped and tested on x86_64-linux. OK for trunk and then for >> release branches? > > OK, but I'm wondering if the same problem can arise when the > handled_component_p includes VIEW_CONVERTs or BIT_FIELD_REFs > both of which may pun to a type already seen in a more inner > referece. SRA already refuses to operate at all on any anything that is accessed with a reference where a V_C_E is not the outermost handled_component. Outermost V_C_Es are skipped and the pass works with the underlying expr. BIT_FIELD_REFs have to be outermost and they are treated similarly. So that should be safe. > Thus, is the actual problem that build_reconstructed_reference > searches for the outermost match of the type rather than the > innermost match? So should it search inner-to-outer instead > (or for the last match in the current way of searching?) I don't think so. In the testcase it found a match where there should have been none (meaning a crude MEM_REF should be created), any certainly correct match must be outside of a union COMPONENT_REF and there should never be more than one. Thanks, Martin > > Thanks, > Richard. > >> Thanks, >> >> Martin >> >> >> gcc/ChangeLog: >> >> 2022-07-01 Martin Jambor <mjambor@suse.cz> >> >> PR tree-optimization/105860 >> * tree-sra.cc (build_reconstructed_reference): Start expr >> traversal only just below the outermost union. >> >> gcc/testsuite/ChangeLog: >> >> 2022-07-01 Martin Jambor <mjambor@suse.cz> >> >> PR tree-optimization/105860 >> * gcc.dg/tree-ssa/alias-access-path-13.c: New test. >> * gcc.dg/tree-ssa/pr105860.c: Likewise. >> --- >> .../gcc.dg/tree-ssa/alias-access-path-13.c | 31 +++++++++ >> gcc/testsuite/gcc.dg/tree-ssa/pr105860.c | 63 +++++++++++++++++++ >> gcc/tree-sra.cc | 13 +++- >> 3 files changed, 106 insertions(+), 1 deletion(-) >> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c >> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr105860.c >> >> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c b/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c >> new file mode 100644 >> index 00000000000..e502a97bc75 >> --- /dev/null >> +++ b/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c >> @@ -0,0 +1,31 @@ >> +/* { dg-do compile } */ >> +/* { dg-options "-O2 -fdump-tree-fre1" } */ >> + >> +struct inn >> +{ >> + int val; >> +}; >> + >> +union foo >> +{ >> + struct inn inn; >> + long int baz; >> +} *fooptr; >> + >> +struct bar >> +{ >> + union foo foo; >> + int val2; >> +} *barptr; >> + >> +int >> +test () >> +{ >> + union foo foo; >> + foo.inn.val = 0; >> + barptr->val2 = 123; >> + *fooptr = foo; >> + return barptr->val2; >> +} >> + >> +/* { dg-final { scan-tree-dump-times "return 123" 1 "fre1"} } */ >> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c b/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c >> new file mode 100644 >> index 00000000000..77bcb4a6739 >> --- /dev/null >> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c >> @@ -0,0 +1,63 @@ >> +/* { dg-do run } */ >> +/* { dg-options "-O1" } */ >> + >> +struct S1 { >> + unsigned int _0; >> + unsigned int _1; >> +} ; >> +struct S2 { >> + struct S1 _s1; >> + unsigned long _x2; >> +} ; >> + >> +struct ufld_type1 { >> + unsigned int _u1t; >> + struct S2 _s2; >> +} ; >> + >> +struct ufld_type2 { >> + unsigned int _u2t; >> + struct S1 _s1; >> +} ; >> +struct parm_type { >> + union { >> + struct ufld_type1 var_1; >> + struct ufld_type2 var_2; >> + } U; >> +}; >> + >> +struct parm_type bad_function( struct parm_type arg0 ) >> +{ >> + struct parm_type rv; >> + struct S2 var4; >> + switch( arg0.U.var_2._u2t ) { >> + case 4294967041: >> + var4._s1 = arg0.U.var_1._s2._s1; >> + rv.U.var_1._u1t = 4294967041; >> + rv.U.var_1._s2 = var4; >> + break; >> + case 4294967043: >> + rv.U.var_2._u2t = 4294967043; >> + rv.U.var_2._s1 = arg0.U.var_2._s1; >> + break; >> + default: >> + break; >> + } >> + return rv; >> +} >> + >> +int main() { >> + struct parm_type val; >> + struct parm_type out; >> + val.U.var_2._u2t = 4294967043; >> + val.U.var_2._s1._0 = 0x01010101; >> + val.U.var_2._s1._1 = 0x02020202; >> + out = bad_function(val); >> + if (val.U.var_2._u2t != 4294967043) >> + __builtin_abort (); >> + if (out.U.var_2._s1._0 != 0x01010101) >> + __builtin_abort (); >> + if (val.U.var_2._s1._1 != 0x02020202 ) >> + __builtin_abort (); >> + return 0; >> +} >> diff --git a/gcc/tree-sra.cc b/gcc/tree-sra.cc >> index 081c51b58a4..099e8dbe873 100644 >> --- a/gcc/tree-sra.cc >> +++ b/gcc/tree-sra.cc >> @@ -1667,7 +1667,18 @@ build_ref_for_offset (location_t loc, tree base, poly_int64 offset, >> static tree >> build_reconstructed_reference (location_t, tree base, struct access *model) >> { >> - tree expr = model->expr, prev_expr = NULL; >> + tree expr = model->expr; >> + /* We have to make sure to start just below the outermost union. */ >> + tree start_expr = expr; >> + while (handled_component_p (expr)) >> + { >> + if (TREE_CODE (TREE_TYPE (TREE_OPERAND (expr, 0))) == UNION_TYPE) >> + start_expr = expr; >> + expr = TREE_OPERAND (expr, 0); >> + } >> + >> + expr = start_expr; >> + tree prev_expr = NULL_TREE; >> while (!types_compatible_p (TREE_TYPE (expr), TREE_TYPE (base))) >> { >> if (!handled_component_p (expr)) >> > > -- > Richard Biener <rguenther@suse.de> > SUSE Software Solutions Germany GmbH, Frankenstra
On Mon, 4 Jul 2022, Martin Jambor wrote: > Hi, > > On Mon, Jul 04 2022, Richard Biener wrote: > > On Fri, 1 Jul 2022, Martin Jambor wrote: > > > >> Hi, > >> > >> As the testcase in PR 105860 shows, the code that tries to re-use the > >> handled_component chains in SRA can be horribly confused by unions, > >> where it thinks it has found a compatible structure under which it can > >> chain the references, but in fact it found the type it was looking > >> for elsewhere in a union and generated a write to a completely wrong > >> part of an aggregate. > >> > >> I don't remember whether the plan was to support unions at all in > >> build_reconstructed_reference but it can work, to an extent, if we > >> make sure that we start the search only outside the outermost union, > >> which is what the patch does (and the extra testcase verifies). > >> > >> Bootstrapped and tested on x86_64-linux. OK for trunk and then for > >> release branches? > > > > OK, but I'm wondering if the same problem can arise when the > > handled_component_p includes VIEW_CONVERTs or BIT_FIELD_REFs > > both of which may pun to a type already seen in a more inner > > referece. > > SRA already refuses to operate at all on any anything that is accessed > with a reference where a V_C_E is not the outermost handled_component. > Outermost V_C_Es are skipped and the pass works with the underlying > expr. BIT_FIELD_REFs have to be outermost and they are treated > similarly. So that should be safe. OK. > > Thus, is the actual problem that build_reconstructed_reference > > searches for the outermost match of the type rather than the > > innermost match? So should it search inner-to-outer instead > > (or for the last match in the current way of searching?) > > I don't think so. In the testcase it found a match where there should > have been none (meaning a crude MEM_REF should be created), any > certainly correct match must be outside of a union COMPONENT_REF and > there should never be more than one. OK, not having looked at the testcase I suspected there would be two matches. I couldn't come up with a case where a single union can confuse things enough .. The patch is OK. Richard. > Thanks, > > Martin > > > > > Thanks, > > Richard. > > > >> Thanks, > >> > >> Martin > >> > >> > >> gcc/ChangeLog: > >> > >> 2022-07-01 Martin Jambor <mjambor@suse.cz> > >> > >> PR tree-optimization/105860 > >> * tree-sra.cc (build_reconstructed_reference): Start expr > >> traversal only just below the outermost union. > >> > >> gcc/testsuite/ChangeLog: > >> > >> 2022-07-01 Martin Jambor <mjambor@suse.cz> > >> > >> PR tree-optimization/105860 > >> * gcc.dg/tree-ssa/alias-access-path-13.c: New test. > >> * gcc.dg/tree-ssa/pr105860.c: Likewise. > >> --- > >> .../gcc.dg/tree-ssa/alias-access-path-13.c | 31 +++++++++ > >> gcc/testsuite/gcc.dg/tree-ssa/pr105860.c | 63 +++++++++++++++++++ > >> gcc/tree-sra.cc | 13 +++- > >> 3 files changed, 106 insertions(+), 1 deletion(-) > >> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c > >> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr105860.c > >> > >> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c b/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c > >> new file mode 100644 > >> index 00000000000..e502a97bc75 > >> --- /dev/null > >> +++ b/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c > >> @@ -0,0 +1,31 @@ > >> +/* { dg-do compile } */ > >> +/* { dg-options "-O2 -fdump-tree-fre1" } */ > >> + > >> +struct inn > >> +{ > >> + int val; > >> +}; > >> + > >> +union foo > >> +{ > >> + struct inn inn; > >> + long int baz; > >> +} *fooptr; > >> + > >> +struct bar > >> +{ > >> + union foo foo; > >> + int val2; > >> +} *barptr; > >> + > >> +int > >> +test () > >> +{ > >> + union foo foo; > >> + foo.inn.val = 0; > >> + barptr->val2 = 123; > >> + *fooptr = foo; > >> + return barptr->val2; > >> +} > >> + > >> +/* { dg-final { scan-tree-dump-times "return 123" 1 "fre1"} } */ > >> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c b/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c > >> new file mode 100644 > >> index 00000000000..77bcb4a6739 > >> --- /dev/null > >> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c > >> @@ -0,0 +1,63 @@ > >> +/* { dg-do run } */ > >> +/* { dg-options "-O1" } */ > >> + > >> +struct S1 { > >> + unsigned int _0; > >> + unsigned int _1; > >> +} ; > >> +struct S2 { > >> + struct S1 _s1; > >> + unsigned long _x2; > >> +} ; > >> + > >> +struct ufld_type1 { > >> + unsigned int _u1t; > >> + struct S2 _s2; > >> +} ; > >> + > >> +struct ufld_type2 { > >> + unsigned int _u2t; > >> + struct S1 _s1; > >> +} ; > >> +struct parm_type { > >> + union { > >> + struct ufld_type1 var_1; > >> + struct ufld_type2 var_2; > >> + } U; > >> +}; > >> + > >> +struct parm_type bad_function( struct parm_type arg0 ) > >> +{ > >> + struct parm_type rv; > >> + struct S2 var4; > >> + switch( arg0.U.var_2._u2t ) { > >> + case 4294967041: > >> + var4._s1 = arg0.U.var_1._s2._s1; > >> + rv.U.var_1._u1t = 4294967041; > >> + rv.U.var_1._s2 = var4; > >> + break; > >> + case 4294967043: > >> + rv.U.var_2._u2t = 4294967043; > >> + rv.U.var_2._s1 = arg0.U.var_2._s1; > >> + break; > >> + default: > >> + break; > >> + } > >> + return rv; > >> +} > >> + > >> +int main() { > >> + struct parm_type val; > >> + struct parm_type out; > >> + val.U.var_2._u2t = 4294967043; > >> + val.U.var_2._s1._0 = 0x01010101; > >> + val.U.var_2._s1._1 = 0x02020202; > >> + out = bad_function(val); > >> + if (val.U.var_2._u2t != 4294967043) > >> + __builtin_abort (); > >> + if (out.U.var_2._s1._0 != 0x01010101) > >> + __builtin_abort (); > >> + if (val.U.var_2._s1._1 != 0x02020202 ) > >> + __builtin_abort (); > >> + return 0; > >> +} > >> diff --git a/gcc/tree-sra.cc b/gcc/tree-sra.cc > >> index 081c51b58a4..099e8dbe873 100644 > >> --- a/gcc/tree-sra.cc > >> +++ b/gcc/tree-sra.cc > >> @@ -1667,7 +1667,18 @@ build_ref_for_offset (location_t loc, tree base, poly_int64 offset, > >> static tree > >> build_reconstructed_reference (location_t, tree base, struct access *model) > >> { > >> - tree expr = model->expr, prev_expr = NULL; > >> + tree expr = model->expr; > >> + /* We have to make sure to start just below the outermost union. */ > >> + tree start_expr = expr; > >> + while (handled_component_p (expr)) > >> + { > >> + if (TREE_CODE (TREE_TYPE (TREE_OPERAND (expr, 0))) == UNION_TYPE) > >> + start_expr = expr; > >> + expr = TREE_OPERAND (expr, 0); > >> + } > >> + > >> + expr = start_expr; > >> + tree prev_expr = NULL_TREE; > >> while (!types_compatible_p (TREE_TYPE (expr), TREE_TYPE (base))) > >> { > >> if (!handled_component_p (expr)) > >> > > > > -- > > Richard Biener <rguenther@suse.de> > > SUSE Software Solutions Germany GmbH, Frankenstra >
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c b/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c new file mode 100644 index 00000000000..e502a97bc75 --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/alias-access-path-13.c @@ -0,0 +1,31 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-fre1" } */ + +struct inn +{ + int val; +}; + +union foo +{ + struct inn inn; + long int baz; +} *fooptr; + +struct bar +{ + union foo foo; + int val2; +} *barptr; + +int +test () +{ + union foo foo; + foo.inn.val = 0; + barptr->val2 = 123; + *fooptr = foo; + return barptr->val2; +} + +/* { dg-final { scan-tree-dump-times "return 123" 1 "fre1"} } */ diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c b/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c new file mode 100644 index 00000000000..77bcb4a6739 --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr105860.c @@ -0,0 +1,63 @@ +/* { dg-do run } */ +/* { dg-options "-O1" } */ + +struct S1 { + unsigned int _0; + unsigned int _1; +} ; +struct S2 { + struct S1 _s1; + unsigned long _x2; +} ; + +struct ufld_type1 { + unsigned int _u1t; + struct S2 _s2; +} ; + +struct ufld_type2 { + unsigned int _u2t; + struct S1 _s1; +} ; +struct parm_type { + union { + struct ufld_type1 var_1; + struct ufld_type2 var_2; + } U; +}; + +struct parm_type bad_function( struct parm_type arg0 ) +{ + struct parm_type rv; + struct S2 var4; + switch( arg0.U.var_2._u2t ) { + case 4294967041: + var4._s1 = arg0.U.var_1._s2._s1; + rv.U.var_1._u1t = 4294967041; + rv.U.var_1._s2 = var4; + break; + case 4294967043: + rv.U.var_2._u2t = 4294967043; + rv.U.var_2._s1 = arg0.U.var_2._s1; + break; + default: + break; + } + return rv; +} + +int main() { + struct parm_type val; + struct parm_type out; + val.U.var_2._u2t = 4294967043; + val.U.var_2._s1._0 = 0x01010101; + val.U.var_2._s1._1 = 0x02020202; + out = bad_function(val); + if (val.U.var_2._u2t != 4294967043) + __builtin_abort (); + if (out.U.var_2._s1._0 != 0x01010101) + __builtin_abort (); + if (val.U.var_2._s1._1 != 0x02020202 ) + __builtin_abort (); + return 0; +} diff --git a/gcc/tree-sra.cc b/gcc/tree-sra.cc index 081c51b58a4..099e8dbe873 100644 --- a/gcc/tree-sra.cc +++ b/gcc/tree-sra.cc @@ -1667,7 +1667,18 @@ build_ref_for_offset (location_t loc, tree base, poly_int64 offset, static tree build_reconstructed_reference (location_t, tree base, struct access *model) { - tree expr = model->expr, prev_expr = NULL; + tree expr = model->expr; + /* We have to make sure to start just below the outermost union. */ + tree start_expr = expr; + while (handled_component_p (expr)) + { + if (TREE_CODE (TREE_TYPE (TREE_OPERAND (expr, 0))) == UNION_TYPE) + start_expr = expr; + expr = TREE_OPERAND (expr, 0); + } + + expr = start_expr; + tree prev_expr = NULL_TREE; while (!types_compatible_p (TREE_TYPE (expr), TREE_TYPE (base))) { if (!handled_component_p (expr))