From: Richard Sandiford Date: Thu, 5 Dec 2019 14:20:38 +0000 (+0000) Subject: Check for bitwise identity when encoding VECTOR_CSTs [PR92768] X-Git-Tag: releases/gcc-9.3.0~108 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2408b93a10c9c6cb210bc2a93d39ce6d56144ca3;p=thirdparty%2Fgcc.git Check for bitwise identity when encoding VECTOR_CSTs [PR92768] This PR shows that we weren't checking for bitwise-identical values when trying to encode a VECTOR_CST, so -0.0 was treated the same as 0.0 for -fno-signed-zeros. The patch adds a new OEP flag to select that behaviour. 2020-02-18 Richard Sandiford gcc/ Backport from mainline 2019-12-05 Richard Sandiford PR middle-end/92768 * tree-core.h (OEP_BITWISE): New flag. * fold-const.c (operand_compare::operand_equal_p): Handle it. * tree-vector-builder.h (tree_vector_builder::equal_p): Pass it. gcc/testsuite/ PR middle-end/92768 * gcc.dg/pr92768.c: New test. --- diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 874de008609f..5cad2832d938 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,13 @@ +2020-02-18 Richard Sandiford + + Backport from mainline + 2019-12-05 Richard Sandiford + + PR middle-end/92768 + * tree-core.h (OEP_BITWISE): New flag. + * fold-const.c (operand_compare::operand_equal_p): Handle it. + * tree-vector-builder.h (tree_vector_builder::equal_p): Pass it. + 2020-02-18 Richard Sandiford Backport from mainline diff --git a/gcc/fold-const.c b/gcc/fold-const.c index 9feaea9fde57..c717f24501e3 100644 --- a/gcc/fold-const.c +++ b/gcc/fold-const.c @@ -2932,6 +2932,11 @@ combine_comparisons (location_t loc, If OEP_LEXICOGRAPHIC is set, then also handle expressions with side-effects such as MODIFY_EXPR, RETURN_EXPR, as well as STATEMENT_LISTs. + If OEP_BITWISE is set, then require the values to be bitwise identical + rather than simply numerically equal. Do not take advantage of things + like math-related flags or undefined behavior; only return true for + values that are provably bitwise identical in all circumstances. + Unless OEP_MATCH_SIDE_EFFECTS is set, the function returns false on any operand with side effect. This is unnecesarily conservative in the case we know that arg0 and arg1 are in disjoint code paths (such as in @@ -2978,6 +2983,11 @@ operand_equal_p (const_tree arg0, const_tree arg1, unsigned int flags) if (!TREE_TYPE (arg0) || !TREE_TYPE (arg1)) return 0; + /* Bitwise identity makes no sense if the values have different layouts. */ + if ((flags & OEP_BITWISE) + && !tree_nop_conversion_p (TREE_TYPE (arg0), TREE_TYPE (arg1))) + return 0; + /* We cannot consider pointers to different address space equal. */ if (POINTER_TYPE_P (TREE_TYPE (arg0)) && POINTER_TYPE_P (TREE_TYPE (arg1)) @@ -3110,8 +3120,7 @@ operand_equal_p (const_tree arg0, const_tree arg1, unsigned int flags) if (real_identical (&TREE_REAL_CST (arg0), &TREE_REAL_CST (arg1))) return 1; - - if (!HONOR_SIGNED_ZEROS (arg0)) + if (!(flags & OEP_BITWISE) && !HONOR_SIGNED_ZEROS (arg0)) { /* If we do not distinguish between signed and unsigned zero, consider them equal. */ @@ -3163,7 +3172,9 @@ operand_equal_p (const_tree arg0, const_tree arg1, unsigned int flags) break; } - if (flags & OEP_ONLY_CONST) + /* Don't handle more cases for OEP_BITWISE, since we can't guarantee that + two instances of undefined behavior will give identical results. */ + if (flags & (OEP_ONLY_CONST | OEP_BITWISE)) return 0; /* Define macros to test an operand from arg0 and arg1 for equality and a diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index d02ad44ceff2..4a17cbdf03d8 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,8 @@ +2020-02-18 Richard Sandiford + + PR middle-end/92768 + * gcc.dg/pr92768.c: New test. + 2020-02-18 Richard Sandiford PR middle-end/90313 diff --git a/gcc/testsuite/gcc.dg/pr92768.c b/gcc/testsuite/gcc.dg/pr92768.c new file mode 100644 index 000000000000..e2a3f9ccacca --- /dev/null +++ b/gcc/testsuite/gcc.dg/pr92768.c @@ -0,0 +1,7 @@ +/* PR tree-optimization/92768 */ +/* { dg-options "-O2 -fno-signed-zeros -fdump-tree-optimized -w -Wno-psabi" } */ + +typedef float v4sf __attribute__((vector_size(16))); +v4sf f () { return (v4sf) { 0.0, -0.0, 0.0, -0.0 }; } + +/* { dg-final { scan-tree-dump {{ 0\.0, -0\.0, 0\.0, -0\.0 }} "optimized" } } */ diff --git a/gcc/tree-core.h b/gcc/tree-core.h index fbed0c379b25..41d052949365 100644 --- a/gcc/tree-core.h +++ b/gcc/tree-core.h @@ -851,7 +851,8 @@ enum operand_equal_flag { /* Internal within inchash::add_expr: */ OEP_HASH_CHECK = 32, /* Makes operand_equal_p handle more expressions: */ - OEP_LEXICOGRAPHIC = 64 + OEP_LEXICOGRAPHIC = 64, + OEP_BITWISE = 128 }; /* Enum and arrays used for tree allocation stats. diff --git a/gcc/tree-vector-builder.h b/gcc/tree-vector-builder.h index 0e36cd171395..13af74ad8340 100644 --- a/gcc/tree-vector-builder.h +++ b/gcc/tree-vector-builder.h @@ -82,7 +82,7 @@ tree_vector_builder::new_vector (tree type, unsigned int npatterns, inline bool tree_vector_builder::equal_p (const_tree elt1, const_tree elt2) const { - return operand_equal_p (elt1, elt2, 0); + return operand_equal_p (elt1, elt2, OEP_BITWISE); } /* Return true if a stepped representation is OK. We don't allow