On Thu, Nov 20, 2014 at 4:21 AM, Patrick Palka <patr...@parcs.ath.cx> wrote: > VRP may simplify a conditional like i <= 5 to i == 5 if it is known that > the lower bound of i's range is 5, e.g. [5, +INF]. But if the upper > bound of i's range is also overflow infinity, i.e. [5, +INF(OVF)] then > this transformation is only valid if -fstrict-overflow is in effect. > Likewise for transforming i > 10 to i != 10 given i's range is > [10, +INF(OVF)] and for transforming i <= 20 to i == 20 given i's range > is [-INF(OVF), 20]. > > This patch makes this transformation only get performed if strict > overflow rules are in effect and potentially emits a -Wstrict-overflow=3 > warning when the transformation takes place. > > Bootstrap and regtesting in progress on x86_64-unknown-linux-gnu. Does > the patch look OK if there are no new regressions?
Ok. Thanks, Richard. > 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. > --- > gcc/testsuite/gcc.dg/no-strict-overflow-8.c | 25 +++++++++++++ > gcc/tree-vrp.c | 57 > +++++++++++++++++++++++++---- > 2 files changed, 74 insertions(+), 8 deletions(-) > create mode 100644 gcc/testsuite/gcc.dg/no-strict-overflow-8.c > > 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 0000000..11ef935 > --- /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 bcf4c2b..444af71 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_CONDITIONAL; > + 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; > } > } > -- > 2.2.0.rc1.23.gf570943 >