| Message ID | alpine.DEB.2.20.11.1603290703070.1308@idea |
|---|---|
| State | New |
| Headers | show |
On Tue, Mar 29, 2016 at 1:23 PM, Patrick Palka <patrick@parcs.ath.cx> wrote: > On Tue, 29 Mar 2016, Richard Biener wrote: > >> On Sun, Mar 27, 2016 at 11:37 PM, Patrick Palka <patrick@parcs.ath.cx> wrote: >> > On Sun, 27 Mar 2016, Patrick Palka wrote: >> > >> >> In unrolling of the inner loop in the test case below we introduce >> >> unreachable code that otherwise contains out-of-bounds array accesses. >> >> This is because the estimation of the maximum number of iterations of >> >> the inner loop is too conservative: we assume 6 iterations instead of >> >> the actual 4. >> >> >> >> Nonetheless, VRP should be able to tell that the code is unreachable so >> >> that it doesn't warn about it. The only thing holding VRP back is that >> >> it doesn't look through conditionals of the form >> >> >> >> if (j_10 != CST1) where j_10 = j_9 + CST2 >> >> >> >> so that it could add the assertion >> >> >> >> j_9 != (CST1 - CST2) >> >> >> >> This patch teaches VRP to detect such conditionals and to add such >> >> assertions, so that it could remove instead of warn about the >> >> unreachable code created during loop unrolling. >> >> >> >> What this addition does with the test case below is something like this: >> >> >> >> ASSERT_EXPR (i <= 5); >> >> for (i = 1; i < 6; i++) >> >> { >> >> j = i - 1; >> >> if (j == 0) >> >> break; >> >> // ASSERT_EXPR (i != 1) >> >> bar[j] = baz[j]; >> >> >> >> j = i - 2 >> >> if (j == 0) >> >> break; >> >> // ASSERT_EXPR (i != 2) >> >> bar[j] = baz[j]; >> >> >> >> j = i - 3 >> >> if (j == 0) >> >> break; >> >> // ASSERT_EXPR (i != 3) >> >> bar[j] = baz[j]; >> >> >> >> j = i - 4 >> >> if (j == 0) >> >> break; >> >> // ASSERT_EXPR (i != 4) >> >> bar[j] = baz[j]; >> >> >> >> j = i - 5 >> >> if (j == 0) >> >> break; >> >> // ASSERT_EXPR (i != 5) >> >> bar[j] = baz[j]; >> >> >> >> j = i - 6 >> >> if (j == 0) >> >> break; >> >> // ASSERT_EXPR (i != 6) >> >> bar[j] = baz[j]; // unreachable because (i != 6 && i <= 5) is always false >> >> } >> >> >> >> (I think the patch I sent a year ago that improved the >> >> register_edge_assert stuff would have fixed this too. I'll try to >> >> post it again during next stage 1. >> >> https://gcc.gnu.org/ml/gcc-patches/2014-11/msg00908.html) >> >> >> >> Bootstrap + regtest in progress on x86_64-pc-linux-gnu, does this look >> >> OK to commit after testing? >> >> >> >> gcc/ChangeLog: >> >> >> >> PR tree-optimization/59124 >> >> * tree-vrp.c (register_edge_assert_for): For NAME != CST1 >> >> where NAME = A + CST2 add the assertion A != (CST1 - CST2). >> >> >> >> gcc/testsuite/ChangeLog: >> >> >> >> PR tree-optimization/59124 >> >> * gcc.dg/Warray-bounds-19.c: New test. >> >> --- >> >> gcc/testsuite/gcc.dg/Warray-bounds-19.c | 17 +++++++++++++++++ >> >> gcc/tree-vrp.c | 22 ++++++++++++++++++++++ >> >> 2 files changed, 39 insertions(+) >> >> create mode 100644 gcc/testsuite/gcc.dg/Warray-bounds-19.c >> >> >> >> diff --git a/gcc/testsuite/gcc.dg/Warray-bounds-19.c b/gcc/testsuite/gcc.dg/Warray-bounds-19.c >> >> new file mode 100644 >> >> index 0000000..e2f9661 >> >> --- /dev/null >> >> +++ b/gcc/testsuite/gcc.dg/Warray-bounds-19.c >> >> @@ -0,0 +1,17 @@ >> >> +/* PR tree-optimization/59124 */ >> >> +/* { dg-options "-O3 -Warray-bounds" } */ >> >> + >> >> +unsigned baz[6]; >> >> + >> >> +void foo(unsigned *bar, unsigned n) >> >> +{ >> >> + unsigned i, j; >> >> + >> >> + if (n > 6) >> >> + n = 6; >> >> + >> >> + for (i = 1; i < n; i++) >> >> + for (j = i - 1; j > 0; j--) >> >> + bar[j - 1] = baz[j - 1]; >> >> +} >> >> + >> >> diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c >> >> index b5654c5..31bd575 100644 >> >> --- a/gcc/tree-vrp.c >> >> +++ b/gcc/tree-vrp.c >> >> @@ -5820,6 +5820,28 @@ register_edge_assert_for (tree name, edge e, gimple_stmt_iterator si, >> >> } >> >> } >> >> >> >> + /* In the case of NAME != CST1 where NAME = A + CST2 we can >> >> + assert that NAME != (CST1 - CST2). */ >> > >> > This should say A != (...) not NAME != (...) >> > >> >> + if ((comp_code == EQ_EXPR || comp_code == NE_EXPR) >> >> + && TREE_CODE (val) == INTEGER_CST) >> >> + { >> >> + gimple *def_stmt = SSA_NAME_DEF_STMT (name); >> >> + >> >> + if (is_gimple_assign (def_stmt) >> >> + && gimple_assign_rhs_code (def_stmt) == PLUS_EXPR) >> >> + { >> >> + tree op0 = gimple_assign_rhs1 (def_stmt); >> >> + tree op1 = gimple_assign_rhs2 (def_stmt); >> >> + if (TREE_CODE (op0) == SSA_NAME >> >> + && TREE_CODE (op1) == INTEGER_CST) >> >> + { >> >> + op1 = int_const_binop (MINUS_EXPR, val, op1); >> >> + register_edge_assert_for_2 (op0, e, si, comp_code, >> >> + op0, op1, is_else_edge); >> > >> > The last argument to register_edge_assert_for_2() should be false not >> > is_else_edge since comp_code is already inverted. >> > >> > Consider these two things fixed. Also I moved down the new code so that >> > it's at the very bottom of register_edge_assert_for. Here's an updated >> > patch that passes bootstrap + regtest. >> > >> > -- 8< -- >> > >> > gcc/ChangeLog: >> > >> > PR tree-optimization/59124 >> > * tree-vrp.c (register_edge_assert_for): For NAME != CST1 >> > where NAME = A + CST2 add the assertion A != (CST1 - CST2). >> > >> > gcc/testsuite/ChangeLog: >> > >> > PR tree-optimization/59124 >> > * gcc.dg/Warray-bounds-19.c: New test. >> > --- >> > gcc/testsuite/gcc.dg/Warray-bounds-19.c | 17 +++++++++++++++++ >> > gcc/tree-vrp.c | 22 ++++++++++++++++++++++ >> > 2 files changed, 39 insertions(+) >> > create mode 100644 gcc/testsuite/gcc.dg/Warray-bounds-19.c >> > >> > diff --git a/gcc/testsuite/gcc.dg/Warray-bounds-19.c b/gcc/testsuite/gcc.dg/Warray-bounds-19.c >> > new file mode 100644 >> > index 0000000..e2f9661 >> > --- /dev/null >> > +++ b/gcc/testsuite/gcc.dg/Warray-bounds-19.c >> > @@ -0,0 +1,17 @@ >> > +/* PR tree-optimization/59124 */ >> > +/* { dg-options "-O3 -Warray-bounds" } */ >> > + >> > +unsigned baz[6]; >> > + >> > +void foo(unsigned *bar, unsigned n) >> > +{ >> > + unsigned i, j; >> > + >> > + if (n > 6) >> > + n = 6; >> > + >> > + for (i = 1; i < n; i++) >> > + for (j = i - 1; j > 0; j--) >> > + bar[j - 1] = baz[j - 1]; >> > +} >> > + >> > diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c >> > index b5654c5..a009f7a 100644 >> > --- a/gcc/tree-vrp.c >> > +++ b/gcc/tree-vrp.c >> > @@ -5841,6 +5841,28 @@ register_edge_assert_for (tree name, edge e, gimple_stmt_iterator si, >> > register_edge_assert_for_1 (op1, EQ_EXPR, e, si); >> > } >> > } >> > + >> > + /* In the case of NAME != CST1 where NAME = A + CST2 we can >> > + assert that A != (CST1 - CST2). */ >> > + if ((comp_code == EQ_EXPR || comp_code == NE_EXPR) >> > + && TREE_CODE (val) == INTEGER_CST) >> > + { >> > + gimple *def_stmt = SSA_NAME_DEF_STMT (name); >> > + >> > + if (is_gimple_assign (def_stmt) >> > + && gimple_assign_rhs_code (def_stmt) == PLUS_EXPR) >> > + { >> > + tree op0 = gimple_assign_rhs1 (def_stmt); >> > + tree op1 = gimple_assign_rhs2 (def_stmt); >> > + if (TREE_CODE (op0) == SSA_NAME >> > + && TREE_CODE (op1) == INTEGER_CST) >> > + { >> > + op1 = int_const_binop (MINUS_EXPR, val, op1); >> >> Please add >> >> if (TREE_OVERFLOW_P (op1)) >> op1 = drop_tree_overflow (op1); >> >> here. > > Done. > >> >> > + register_edge_assert_for_2 (op0, e, si, comp_code, >> > + op0, op1, false); >> >> I wonder why you recurse to register_edge_assert_for_2 here rather than >> calling register_new_assert_for which is what the cases in >> register_edge_assert_for_2 >> do. And incidentially a more generic case of this pattern is handled >> there, so why >> not add this code in register_edge_assert_for_2 in the first place? There is >> >> >> if (TREE_CODE_CLASS (comp_code) == tcc_comparison >> && TREE_CODE (val) == INTEGER_CST) >> { >> gimple *def_stmt = SSA_NAME_DEF_STMT (name); >> ... >> >> the case itself is simple enough to be worth adding to fix the regression. > > Done. I figured recursing would help to identify other useful > assertions to add but it's not necessary to fix the test case. > >> >> I also wonder why we don't have a match.pd / fold-const case for this, >> the forwprop pass between cunrolli and vrp1 should have simplified >> this then. fold_comparison has it (so it didn't get moved to match.pd): >> >> /* Transform comparisons of the form X +- C1 CMP C2 to X CMP C2 -+ C1. */ >> if ((TREE_CODE (arg0) == PLUS_EXPR || TREE_CODE (arg0) == MINUS_EXPR) >> && (equality_code >> ... >> >> it's also more general in that it handles non-equality compares when overflow >> is undefined. Note that at this stage I'm more comfortable with doing the >> VRP trick than adding a new match.pd pattern (even if only handling the >> equality compare case) - we'd need to think about what to exactly do >> for a non-single-use case (probably depends on C2, if that's zero then >> X +- C1 might set CC codes properly already). > > The operands in question are not single-use and C2 is zero so we'd > already be hitting the edge case :( Bah ... :/ > Here's an updated patch that calls drop_tree_overflow and moves it all > to register_edge_assert_for_2. Does this look OK to commit after > bootstrap and regtest? Ok - bonus points if you handle MINUS_EXPR for symmetry reasons even if not strictly necessary at this point. Thanks, Richard. > -- >8 -- > > gcc/ChangeLog: > > PR tree-optimization/59124 > * tree-vrp.c (register_edge_assert_for_2): For NAME != CST1 > where NAME = A + CST2 add the assertion A != (CST1 - CST2). > > gcc/testsuite/ChangeLog: > > PR tree-optimization/59124 > * gcc.dg/Warray-bounds-19.c: New test. > --- > gcc/testsuite/gcc.dg/Warray-bounds-19.c | 17 +++++++++++++++++ > gcc/tree-vrp.c | 19 +++++++++++++++++++ > 2 files changed, 36 insertions(+) > create mode 100644 gcc/testsuite/gcc.dg/Warray-bounds-19.c > > diff --git a/gcc/testsuite/gcc.dg/Warray-bounds-19.c b/gcc/testsuite/gcc.dg/Warray-bounds-19.c > new file mode 100644 > index 0000000..e2f9661 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/Warray-bounds-19.c > @@ -0,0 +1,17 @@ > +/* PR tree-optimization/59124 */ > +/* { dg-options "-O3 -Warray-bounds" } */ > + > +unsigned baz[6]; > + > +void foo(unsigned *bar, unsigned n) > +{ > + unsigned i, j; > + > + if (n > 6) > + n = 6; > + > + for (i = 1; i < n; i++) > + for (j = i - 1; j > 0; j--) > + bar[j - 1] = baz[j - 1]; > +} > + > diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c > index b5654c5..87db548 100644 > --- a/gcc/tree-vrp.c > +++ b/gcc/tree-vrp.c > @@ -5310,6 +5310,25 @@ register_edge_assert_for_2 (tree name, edge e, gimple_stmt_iterator bsi, > if (is_gimple_assign (def_stmt)) > rhs_code = gimple_assign_rhs_code (def_stmt); > > + /* In the case of NAME != CST1 where NAME = A + CST2 we can > + assert that A != (CST1 - CST2). */ > + if ((comp_code == EQ_EXPR || comp_code == NE_EXPR) > + && rhs_code == PLUS_EXPR) > + { > + tree op0 = gimple_assign_rhs1 (def_stmt); > + tree op1 = gimple_assign_rhs2 (def_stmt); > + if (TREE_CODE (op0) == SSA_NAME > + && TREE_CODE (op1) == INTEGER_CST > + && live_on_edge (e, op0) > + && !has_single_use (op0)) > + { > + op1 = int_const_binop (MINUS_EXPR, val, op1); > + if (TREE_OVERFLOW (op1)) > + op1 = drop_tree_overflow (op1); > + register_new_assert_for (op0, op0, comp_code, op1, NULL, e, bsi); > + } > + } > + > /* Add asserts for NAME cmp CST and NAME being defined > as NAME = (int) NAME2. */ > if (!TYPE_UNSIGNED (TREE_TYPE (val)) > -- > 2.8.0.rc3.27.gade0865 >
diff --git a/gcc/testsuite/gcc.dg/Warray-bounds-19.c b/gcc/testsuite/gcc.dg/Warray-bounds-19.c new file mode 100644 index 0000000..e2f9661 --- /dev/null +++ b/gcc/testsuite/gcc.dg/Warray-bounds-19.c @@ -0,0 +1,17 @@ +/* PR tree-optimization/59124 */ +/* { dg-options "-O3 -Warray-bounds" } */ + +unsigned baz[6]; + +void foo(unsigned *bar, unsigned n) +{ + unsigned i, j; + + if (n > 6) + n = 6; + + for (i = 1; i < n; i++) + for (j = i - 1; j > 0; j--) + bar[j - 1] = baz[j - 1]; +} + diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c index b5654c5..87db548 100644 --- a/gcc/tree-vrp.c +++ b/gcc/tree-vrp.c @@ -5310,6 +5310,25 @@ register_edge_assert_for_2 (tree name, edge e, gimple_stmt_iterator bsi, if (is_gimple_assign (def_stmt)) rhs_code = gimple_assign_rhs_code (def_stmt); + /* In the case of NAME != CST1 where NAME = A + CST2 we can + assert that A != (CST1 - CST2). */ + if ((comp_code == EQ_EXPR || comp_code == NE_EXPR) + && rhs_code == PLUS_EXPR) + { + tree op0 = gimple_assign_rhs1 (def_stmt); + tree op1 = gimple_assign_rhs2 (def_stmt); + if (TREE_CODE (op0) == SSA_NAME + && TREE_CODE (op1) == INTEGER_CST + && live_on_edge (e, op0) + && !has_single_use (op0)) + { + op1 = int_const_binop (MINUS_EXPR, val, op1); + if (TREE_OVERFLOW (op1)) + op1 = drop_tree_overflow (op1); + register_new_assert_for (op0, op0, comp_code, op1, NULL, e, bsi); + } + } + /* Add asserts for NAME cmp CST and NAME being defined as NAME = (int) NAME2. */ if (!TYPE_UNSIGNED (TREE_TYPE (val))