From 7ac753f9683133e7b91f2d497ab6b25418a05c5d Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Thu, 20 Nov 2014 22:25:35 +0000 Subject: [PATCH] Disable an unsafe VRP transformation when -fno-strict-overflow is set gcc/ * tree-vrp.c (test_for_singularity): New parameter strict_overflow_p. Set *strict_overflow_p to true if signed overflow must be undefined for the return value to satisfy the conditional. (simplify_cond_using_ranges): Don't perform the simplification if it violates overflow rules. gcc/testsuite/ * gcc.dg/no-strict-overflow-8.c: New test. From-SVN: r217895 --- gcc/ChangeLog | 9 ++++ gcc/testsuite/ChangeLog | 4 ++ gcc/testsuite/gcc.dg/no-strict-overflow-8.c | 25 +++++++++ gcc/tree-vrp.c | 57 ++++++++++++++++++--- 4 files changed, 87 insertions(+), 8 deletions(-) create mode 100644 gcc/testsuite/gcc.dg/no-strict-overflow-8.c diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 394ae4fd442..4501014d340 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,12 @@ +2014-11-20 Patrick Palka + + * tree-vrp.c (test_for_singularity): New parameter + strict_overflow_p. Set *strict_overflow_p to true if signed + overflow must be undefined for the return value to satisfy the + conditional. + (simplify_cond_using_ranges): Don't perform the simplification + if it violates overflow rules. + 2014-11-20 Marek Polacek * tree-ssa-loop-niter.c (maybe_lower_iteration_bound): Fix typo. diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index 4aba5fb9e86..882e2ac4e82 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,7 @@ +2014-11-20 Patrick Palka + + * gcc.dg/no-strict-overflow-8.c: New test. + 2014-11-20 Andrew Stubbs * gcc.dg/undefined-loop-1.c: New file. diff --git a/gcc/testsuite/gcc.dg/no-strict-overflow-8.c b/gcc/testsuite/gcc.dg/no-strict-overflow-8.c new file mode 100644 index 00000000000..11ef9358d5a --- /dev/null +++ b/gcc/testsuite/gcc.dg/no-strict-overflow-8.c @@ -0,0 +1,25 @@ +/* { dg-do compile } */ +/* { dg-options "-fno-strict-overflow -O2 -fdump-tree-optimized" } */ + +/* We cannot fold i > 0 because p->a - p->b can be larger than INT_MAX + and thus i can wrap. Dual of Wstrict-overflow-18.c */ + +struct c { unsigned int a; unsigned int b; }; +extern void bar (struct c *); +int +foo (struct c *p) +{ + int i; + int sum = 0; + + for (i = 0; i < p->a - p->b; ++i) + { + if (i > 0) + sum += 2; + bar (p); + } + return sum; +} + +/* { dg-final { scan-tree-dump "i_.* > 0" "optimized" } } */ +/* { dg-final { cleanup-tree-dump "optimized" } } */ diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c index bcf4c2ba60c..a75138ffc5b 100644 --- a/gcc/tree-vrp.c +++ b/gcc/tree-vrp.c @@ -9117,11 +9117,15 @@ simplify_bit_ops_using_ranges (gimple_stmt_iterator *gsi, gimple stmt) a known value range VR. If there is one and only one value which will satisfy the - conditional, then return that value. Else return NULL. */ + conditional, then return that value. Else return NULL. + + If signed overflow must be undefined for the value to satisfy + the conditional, then set *STRICT_OVERFLOW_P to true. */ static tree test_for_singularity (enum tree_code cond_code, tree op0, - tree op1, value_range_t *vr) + tree op1, value_range_t *vr, + bool *strict_overflow_p) { tree min = NULL; tree max = NULL; @@ -9172,7 +9176,16 @@ test_for_singularity (enum tree_code cond_code, tree op0, then there is only one value which can satisfy the condition, return that value. */ if (operand_equal_p (min, max, 0) && is_gimple_min_invariant (min)) - return min; + { + if ((cond_code == LE_EXPR || cond_code == LT_EXPR) + && is_overflow_infinity (vr->max)) + *strict_overflow_p = true; + if ((cond_code == GE_EXPR || cond_code == GT_EXPR) + && is_overflow_infinity (vr->min)) + *strict_overflow_p = true; + + return min; + } } return NULL; } @@ -9252,9 +9265,12 @@ simplify_cond_using_ranges (gcond *stmt) able to simplify this conditional. */ if (vr->type == VR_RANGE) { - tree new_tree = test_for_singularity (cond_code, op0, op1, vr); + enum warn_strict_overflow_code wc = WARN_STRICT_OVERFLOW_COMPARISON; + bool sop = false; + tree new_tree = test_for_singularity (cond_code, op0, op1, vr, &sop); - if (new_tree) + if (new_tree + && (!sop || TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (op0)))) { if (dump_file) { @@ -9275,16 +9291,30 @@ simplify_cond_using_ranges (gcond *stmt) fprintf (dump_file, "\n"); } + if (sop && issue_strict_overflow_warning (wc)) + { + location_t location = input_location; + if (gimple_has_location (stmt)) + location = gimple_location (stmt); + + warning_at (location, OPT_Wstrict_overflow, + "assuming signed overflow does not occur when " + "simplifying conditional"); + } + return true; } /* Try again after inverting the condition. We only deal with integral types here, so no need to worry about issues with inverting FP comparisons. */ - cond_code = invert_tree_comparison (cond_code, false); - new_tree = test_for_singularity (cond_code, op0, op1, vr); + sop = false; + new_tree = test_for_singularity + (invert_tree_comparison (cond_code, false), + op0, op1, vr, &sop); - if (new_tree) + if (new_tree + && (!sop || TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (op0)))) { if (dump_file) { @@ -9305,6 +9335,17 @@ simplify_cond_using_ranges (gcond *stmt) fprintf (dump_file, "\n"); } + if (sop && issue_strict_overflow_warning (wc)) + { + location_t location = input_location; + if (gimple_has_location (stmt)) + location = gimple_location (stmt); + + warning_at (location, OPT_Wstrict_overflow, + "assuming signed overflow does not occur when " + "simplifying conditional"); + } + return true; } } -- 2.30.2