https://gcc.gnu.org/g:8add706704470554130f04b63e6ea440a171b747
commit r17-2480-g8add706704470554130f04b63e6ea440a171b747 Author: H.J. Lu <[email protected]> Date: Thu Jul 16 05:39:33 2026 +0800 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]> Diff: --- gcc/config/i386/i386-expand.cc | 14 ++++++++----- gcc/testsuite/gcc.target/i386/pr126275.c | 36 ++++++++++++++++++++++++++++++++ 2 files changed, 45 insertions(+), 5 deletions(-) diff --git a/gcc/config/i386/i386-expand.cc b/gcc/config/i386/i386-expand.cc index a448e470f737..fceb958b7e6a 100644 --- a/gcc/config/i386/i386-expand.cc +++ b/gcc/config/i386/i386-expand.cc @@ -9765,11 +9765,15 @@ 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 HOST_WIDE_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 000000000000..21457bed0404 --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/pr126275.c @@ -0,0 +1,36 @@ +/* { dg-do compile } */ +/* { 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; +}
