Various optimizations in fold_inf_compare can cause "invalid" floating-point exceptions to be present when they should be absent, or vice versa. Folding x > +Inf to 0 should not be about HONOR_SNANS - ordered comparisons of both quiet and signaling NaNs should raise invalid. So if -ftrapping-math and HONOR_NANS, this is invalid (given a strict interpretation of -ftrapping-math, anyway). x <= +Inf is not the same as x == x, because again that loses an exception (equality comparisons don't raise exceptions except for signaling NaNs). x == +Inf is not the same as x > DBL_MAX, and a similar issue applies with the x != +Inf case - that transformation causes a spurious exception (in particular, I've seen this in __gcc_qadd for powerpc-linux-gnu soft-float, causing glibc testsuite failures, which is how I found this bug), not just a missing exception. (The existing HONOR_NANS code for NE_EXPR is only about the result, not the exceptions raised.)
Author: jsm28 Date: Tue Jan 9 13:25:38 2018 New Revision: 256380 URL: https://gcc.gnu.org/viewcvs?rev=256380&root=gcc&view=rev Log: Fix folding of Inf/NaN comparisons for -ftrapping-math (PR tree-optimization/64811). The folding of comparisons against Inf (to constants or comparisons with the maximum finite value) has various cases where it introduces or loses "invalid" exceptions for comparisons with NaNs. Folding x > +Inf to 0 should not be about HONOR_SNANS - ordered comparisons of both quiet and signaling NaNs should raise invalid. x <= +Inf is not the same as x == x, because again that loses an exception (equality comparisons don't raise exceptions except for signaling NaNs). x == +Inf is not the same as x > DBL_MAX, and a similar issue applies with the x != +Inf case - that transformation causes a spurious exception. This patch fixes the conditionals on the folding to avoid such introducing or losing exceptions. Bootstrapped with no regressions on x86_64-pc-linux-gnu (where the cases involving spurious exceptions wouldn't have failed anyway before GCC 8 because of unordered comparisons wrongly always having formerly been used by the back end). Also tested for powerpc-linux-gnu soft-float that this fixes many glibc math/ test failures that arose in that configuration because this folding affected the IBM long double support in libgcc (no such failures appeared for hard-float because of the bug of powerpc hard-float always using unordered comparisons) - some failures remain, but I believe them to be unrelated. PR tree-optimization/64811 gcc: * match.pd: When optimizing comparisons with Inf, avoid introducing or losing exceptions from comparisons with NaN. gcc/testsuite: * gcc.dg/torture/inf-compare-1.c, gcc.dg/torture/inf-compare-2.c, gcc.dg/torture/inf-compare-3.c, gcc.dg/torture/inf-compare-4.c, gcc.dg/torture/inf-compare-5.c, gcc.dg/torture/inf-compare-6.c, gcc.dg/torture/inf-compare-7.c, gcc.dg/torture/inf-compare-8.c: New tests. * gcc.c-torture/execute/ieee/fp-cmp-7.x: New file. Added: trunk/gcc/testsuite/gcc.c-torture/execute/ieee/fp-cmp-7.x trunk/gcc/testsuite/gcc.dg/torture/inf-compare-1.c trunk/gcc/testsuite/gcc.dg/torture/inf-compare-2.c trunk/gcc/testsuite/gcc.dg/torture/inf-compare-3.c trunk/gcc/testsuite/gcc.dg/torture/inf-compare-4.c trunk/gcc/testsuite/gcc.dg/torture/inf-compare-5.c trunk/gcc/testsuite/gcc.dg/torture/inf-compare-6.c trunk/gcc/testsuite/gcc.dg/torture/inf-compare-7.c trunk/gcc/testsuite/gcc.dg/torture/inf-compare-8.c Modified: trunk/gcc/ChangeLog trunk/gcc/match.pd trunk/gcc/testsuite/ChangeLog
Fixed for GCC 8.