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| author | Roger Sayle <roger@nextmovesoftware.com> | 2022-03-11 17:46:50 +0000 |
|---|---|---|
| committer | Roger Sayle <roger@nextmovesoftware.com> | 2022-03-11 17:51:18 +0000 |
| commit | c5288df751f9ecd11898dec5f2a7b6b03267f79e (patch) | |
| tree | 6ba408ab136ef26fb762ca5138c9958f341f1529 /gcc/tree-ssa-alias.h | |
| parent | 098c538ae8c0c5e281d9191a6b54ffe38b624ef3 (diff) | |
| download | gcc-c5288df751f9ecd11898dec5f2a7b6b03267f79e.zip gcc-c5288df751f9ecd11898dec5f2a7b6b03267f79e.tar.gz gcc-c5288df751f9ecd11898dec5f2a7b6b03267f79e.tar.bz2 | |
PR tree-optimization/98335: Improvements to DSE's compute_trims.
This patch is the main middle-end piece of a fix for PR tree-opt/98335,
which is a code-quality regression affecting mainline. The issue occurs
in DSE's (dead store elimination's) compute_trims function that determines
where a store to memory can be trimmed. In the testcase given in the
PR, this function notices that the first byte of a DImode store is dead,
and replaces the 8-byte store at (aligned) offset zero, with a 7-byte store
at (unaligned) offset one. Most architectures can store a power-of-two
bytes (up to a maximum) in single instruction, so writing 7 bytes requires
more instructions than writing 8 bytes. This patch follows Jakub Jelinek's
suggestion in comment 5, that compute_trims needs improved heuristics.
On x86_64-pc-linux-gnu with -O2 the new test case in the PR goes from:
movl $0, -24(%rsp)
movabsq $72057594037927935, %rdx
movl $0, -21(%rsp)
andq -24(%rsp), %rdx
movq %rdx, %rax
salq $8, %rax
movb c(%rip), %al
ret
to
xorl %eax, %eax
movb c(%rip), %al
ret
2022-03-11 Roger Sayle <roger@nextmovesoftware.com>
Richard Biener <rguenther@suse.de>
gcc/ChangeLog
PR tree-optimization/98335
* builtins.cc (get_object_alignment_2): Export.
* builtins.h (get_object_alignment_2): Likewise.
* tree-ssa-alias.cc (ao_ref_alignment): New.
* tree-ssa-alias.h (ao_ref_alignment): Declare.
* tree-ssa-dse.cc (compute_trims): Improve logic deciding whether
to align head/tail, writing more bytes but using fewer store insns.
gcc/testsuite/ChangeLog
PR tree-optimization/98335
* g++.dg/pr98335.C: New test case.
* gcc.dg/pr86010.c: New test case.
* gcc.dg/pr86010-2.c: New test case.
Diffstat (limited to 'gcc/tree-ssa-alias.h')
| -rw-r--r-- | gcc/tree-ssa-alias.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/gcc/tree-ssa-alias.h b/gcc/tree-ssa-alias.h index 6ae1a65..dfb2127 100644 --- a/gcc/tree-ssa-alias.h +++ b/gcc/tree-ssa-alias.h @@ -119,6 +119,8 @@ extern alias_set_type ao_ref_alias_set (ao_ref *); extern alias_set_type ao_ref_base_alias_set (ao_ref *); extern tree ao_ref_alias_ptr_type (ao_ref *); extern tree ao_ref_base_alias_ptr_type (ao_ref *); +extern bool ao_ref_alignment (ao_ref *, unsigned int *, + unsigned HOST_WIDE_INT *); extern bool ptr_deref_may_alias_global_p (tree); extern bool ptr_derefs_may_alias_p (tree, tree); extern bool ptrs_compare_unequal (tree, tree); |