From 08dfb1d682a707f7319aafec28edda424395dae5 Mon Sep 17 00:00:00 2001 From: Richard Biener Date: Mon, 8 Jul 2019 11:46:26 +0000 Subject: [PATCH] re PR tree-optimization/91108 (Fails to pun through unions) 2019-07-08 Richard Biener PR tree-optimization/91108 * tree-ssa-sccvn.c: Include builtins.h. (vn_reference_lookup_3): Use only alignment constraints to verify same-valued store disambiguation. * gcc.dg/tree-ssa/ssa-fre-61.c: Adjust back. * gcc.dg/tree-ssa/ssa-fre-78.c: New testcase. From-SVN: r273232 --- gcc/testsuite/ChangeLog | 6 +++++ gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-61.c | 2 +- gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-78.c | 27 +++++++++++++++++++ gcc/tree-ssa-sccvn.c | 30 +++++++++------------- 4 files changed, 46 insertions(+), 19 deletions(-) create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-78.c diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index 56f2f2c5964..dbe70b9a98e 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,9 @@ +2019-07-08 Richard Biener + + PR tree-optimization/91108 + * gcc.dg/tree-ssa/ssa-fre-61.c: Adjust back. + * gcc.dg/tree-ssa/ssa-fre-78.c: New testcase. + 2019-07-08 Jim Wilson * gcc.target/riscv/shift-shift-2.c: Add one more test. diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-61.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-61.c index eae4b15b7f2..a4d9a7194bf 100644 --- a/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-61.c +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-61.c @@ -1,5 +1,5 @@ /* { dg-do link } */ -/* { dg-options "-O -fstrict-aliasing -fdump-tree-fre1-details" } */ +/* { dg-options "-O -fdump-tree-fre1-details" } */ void link_error (void); diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-78.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-78.c new file mode 100644 index 00000000000..4ad232ea123 --- /dev/null +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-78.c @@ -0,0 +1,27 @@ +/* { dg-do run } */ +/* { dg-options "-O3 -fstrict-aliasing" } */ + +union U { + struct A { int : 2; int x : 8; } a; + struct B { int : 6; int x : 8; } b; +}; + +int __attribute__((noipa)) +foo (union U *p, union U *q) +{ + p->a.x = 1; + q->b.x = 1; + return p->a.x; +} + +int +main() +{ + union U x; + if (foo (&x, &x) != x.a.x) + __builtin_abort (); + return 0; +} + +/* We support arbitrary punning through unions when it happens through + the union type and thus p == q is valid here. */ diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c index 3c45adcf326..854222a0cc2 100644 --- a/gcc/tree-ssa-sccvn.c +++ b/gcc/tree-ssa-sccvn.c @@ -70,6 +70,7 @@ along with GCC; see the file COPYING3. If not see #include "tree-ssa-loop.h" #include "tree-scalar-evolution.h" #include "tree-ssa-loop-niter.h" +#include "builtins.h" #include "tree-ssa-sccvn.h" /* This algorithm is based on the SCC algorithm presented by Keith @@ -2248,24 +2249,10 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_, /* If we reach a clobbering statement try to skip it and see if we find a VN result with exactly the same value as the possible clobber. In this case we can ignore the clobber - and return the found value. - Note that we don't need to worry about partial overlapping - accesses as we then can use TBAA to disambiguate against the - clobbering statement when looking up a load (thus the - VN_WALKREWRITE guard). */ - if (data->vn_walk_kind == VN_WALKREWRITE - && is_gimple_reg_type (TREE_TYPE (lhs)) + and return the found value. */ + if (is_gimple_reg_type (TREE_TYPE (lhs)) && types_compatible_p (TREE_TYPE (lhs), vr->type) - /* The overlap restriction breaks down when either access - alias-set is zero. Still for accesses of the size of - an addressable unit there can be no overlaps. Overlaps - between different union members are not an issue since - activation of a union member via a store makes the - values of untouched bytes unspecified. */ - && (known_eq (ref->size, BITS_PER_UNIT) - || (flag_strict_aliasing - && get_alias_set (lhs) != 0 - && ao_ref_alias_set (ref) != 0))) + && ref->ref) { tree *saved_last_vuse_ptr = data->last_vuse_ptr; /* Do not update last_vuse_ptr in vn_reference_lookup_2. */ @@ -2284,7 +2271,14 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_, if (TREE_CODE (rhs) == SSA_NAME) rhs = SSA_VAL (rhs); if (vnresult->result - && operand_equal_p (vnresult->result, rhs, 0)) + && operand_equal_p (vnresult->result, rhs, 0) + /* We have to honor our promise about union type punning + and also support arbitrary overlaps with + -fno-strict-aliasing. So simply resort to alignment to + rule out overlaps. Do this check last because it is + quite expensive compared to the hash-lookup above. */ + && multiple_p (get_object_alignment (ref->ref), ref->size) + && multiple_p (get_object_alignment (lhs), ref->size)) return res; } } -- 2.30.2