After
commit cbc56384029c9224280b0a1018fb9502797f243d
Author: H.J. Lu <[email protected]>
Date: Fri Jun 26 08:43:20 2026 +0800
determine_block_size: Set len_rtx to min size if min size == max size
ix86_expand_set_or_cpymem may use vector loop on a block of memory whose
size < epilogue size. Don't use misaligned prologue if count <= epilogue
size.
gcc/
PR target/126275
* config/i386/i386-expand.cc (ix86_expand_set_or_cpymem): Don't
use misaligned prologue if count <= epilogue size.
gcc/testsuite/
PR target/126275
* gcc.target/i386/pr126275.c: New.
--
H.J.
From e638d794f466922cbbcb1dd15ca68324da756207 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <[email protected]>
Date: Thu, 16 Jul 2026 05:39:33 +0800
Subject: [PATCH] x86: Avoid misaligned prologue if count <= epilogue size
After
commit cbc56384029c9224280b0a1018fb9502797f243d
Author: H.J. Lu <[email protected]>
Date: Fri Jun 26 08:43:20 2026 +0800
determine_block_size: Set len_rtx to min size if min size == max size
ix86_expand_set_or_cpymem may use vector loop on a block of memory whose
size < epilogue size. Don't use misaligned prologue if count <= epilogue
size.
gcc/
PR target/126275
* config/i386/i386-expand.cc (ix86_expand_set_or_cpymem): Don't
use misaligned prologue if count <= epilogue size.
gcc/testsuite/
PR target/126275
* gcc.target/i386/pr126275.c: New.
Signed-off-by: H.J. Lu <[email protected]>
---
gcc/config/i386/i386-expand.cc | 13 +++++----
gcc/testsuite/gcc.target/i386/pr126275.c | 36 ++++++++++++++++++++++++
2 files changed, 44 insertions(+), 5 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/i386/pr126275.c
diff --git a/gcc/config/i386/i386-expand.cc b/gcc/config/i386/i386-expand.cc
index 2f6b401e3ab..1841428b3dc 100644
--- a/gcc/config/i386/i386-expand.cc
+++ b/gcc/config/i386/i386-expand.cc
@@ -9765,11 +9765,14 @@ ix86_expand_set_or_cpymem (rtx dst, rtx src, rtx count_exp, rtx val_exp,
/* Destination is aligned after the misaligned prologue. */
aligned_dstmem = misaligned_prologue_used;
- if (noalign && !misaligned_prologue_used)
- {
- /* Also use misaligned prologue if alignment isn't needed and
- destination isn't aligned. Since alignment isn't needed,
- the destination after prologue won't be aligned. */
+ if (noalign
+ && !misaligned_prologue_used
+ && (!count || count > (unsigned int) epilogue_size_needed))
+ {
+ /* Also use misaligned prologue if count > epilogue size,
+ alignment isn't needed and destination isn't aligned.
+ Since alignment isn't needed, the destination after
+ prologue won't be aligned. */
aligned_dstmem = (GET_MODE_ALIGNMENT (move_mode)
<= MEM_ALIGN (dst));
if (!aligned_dstmem)
diff --git a/gcc/testsuite/gcc.target/i386/pr126275.c b/gcc/testsuite/gcc.target/i386/pr126275.c
new file mode 100644
index 00000000000..c57cc0ebd0a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr126275.c
@@ -0,0 +1,36 @@
+/* { dg-do compile { target fpic } } */
+/* { dg-options "-O1 -fno-pic -ftree-loop-distribute-patterns -fno-tree-dominator-opts -fno-tree-scev-cprop -march=x86-64" } */
+
+/* Keep labels and directives ('.cfi_startproc', '.cfi_endproc'). */
+/* { dg-final { check-function-bodies "**" "" "" { target { *-*-linux* && lp64 } } {^\t?\.} } } */
+
+/*
+**func:
+**.LFB0:
+** .cfi_startproc
+** movl \$0, %eax
+** .p2align 3
+**.L2:
+** addl \$1, %eax
+** cmpl \$18, %eax
+** jne .L2
+** cltq
+** movabsq \$506381209866536711, %rdx
+** movq %rdx, %xmm0
+** punpcklqdq %xmm0, %xmm0
+** movups %xmm0, buf\(%rax\)
+** movb \$7, buf\+16\(%rax\)
+** ret
+** .cfi_endproc
+**...
+*/
+
+extern char buf[512];
+
+void
+func (void)
+{
+ int i = 0;
+ for (; i < 18; i++);
+ for (; i < 35; i++) buf[i] = 7;
+}
--
2.55.0
