From 468e1ef4be47810052687c8193d106e591c74bc4 Mon Sep 17 00:00:00 2001 From: Alexandre Oliva Date: Thu, 20 Sep 2018 19:34:44 +0000 Subject: [PATCH] [PR87054] fix unaligned access Building an ADDR_EXPR uses the canonical type to build the pointer type, but then, as we dereference it, we lose track of lax alignment known to apply to the dereferenced object. This might not be a problem in general, but it is when the compiler implicitly introduces address taking and dereferencing, as it does for asm statements, and as it may do in some loop optimizations. From: Richard Biener for gcc/ChangeLog PR middle-end/87054 * gimplify.c (gimplify_expr): Retain alignment of addressable lvalue in dereference. From: Alexandre Oliva for gcc/testsuite/ChangeLog PR middle-end/87054 * gcc.dg/pr87054.c: New. From-SVN: r264450 --- gcc/ChangeLog | 6 ++++++ gcc/gimplify.c | 8 +++++++- gcc/testsuite/ChangeLog | 5 +++++ gcc/testsuite/gcc.dg/pr87054.c | 29 +++++++++++++++++++++++++++++ 4 files changed, 47 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/gcc.dg/pr87054.c diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 641e3591040..361dfc468a1 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,9 @@ +2018-09-20 Richard Biener + + PR middle-end/87054 + * gimplify.c (gimplify_expr): Retain alignment of + addressable lvalue in dereference. + 2018-09-20 Alexandre Oliva PR bootstrap/87013 diff --git a/gcc/gimplify.c b/gcc/gimplify.c index f0eb04a751c..509fc2f3f5b 100644 --- a/gcc/gimplify.c +++ b/gcc/gimplify.c @@ -12538,9 +12538,15 @@ gimplify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p, /* An lvalue will do. Take the address of the expression, store it in a temporary, and replace the expression with an INDIRECT_REF of that temporary. */ + tree ref_alias_type = reference_alias_ptr_type (*expr_p); + unsigned int ref_align = get_object_alignment (*expr_p); + tree ref_type = TREE_TYPE (*expr_p); tmp = build_fold_addr_expr_loc (input_location, *expr_p); gimplify_expr (&tmp, pre_p, post_p, is_gimple_reg, fb_rvalue); - *expr_p = build_simple_mem_ref (tmp); + if (TYPE_ALIGN (ref_type) != ref_align) + ref_type = build_aligned_type (ref_type, ref_align); + *expr_p = build2 (MEM_REF, ref_type, + tmp, build_zero_cst (ref_alias_type)); } else if ((fallback & fb_rvalue) && is_gimple_reg_rhs_or_call (*expr_p)) { diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index c7c8e90b27c..a0a08a4d499 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,8 @@ +2018-09-20 Alexandre Oliva + + PR middle-end/87054 + * gcc.dg/pr87054.c: New. + 2018-09-20 Richard Sandiford PR tree-optimization/87288 diff --git a/gcc/testsuite/gcc.dg/pr87054.c b/gcc/testsuite/gcc.dg/pr87054.c new file mode 100644 index 00000000000..4ca2b62d2c7 --- /dev/null +++ b/gcc/testsuite/gcc.dg/pr87054.c @@ -0,0 +1,29 @@ +// { dg-do run } +// { dg-options "-O2" } + +#ifndef T +# ifdef __SSE__ +# define T __int128 +# else +# define T long +# endif +#endif +#ifndef R +# ifdef __SSE__ +# define R "x" +# else +# define R "r" +# endif +#endif + + +typedef T A; // #define T to long or __int128 +struct B { char d; A c; } __attribute__((packed)); +struct B b[50]; // many elements to avoid loop unrolling + +int main () { + int i; + for (i = 0; i < sizeof(b) / sizeof(*b); i++) { + asm ("" : "+" R (b[i].c)); // #define R to "r" on ppc or "x" on x86_64 + } +}