| Message ID | 20211023052647.535991-1-goldstein.w.n@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v1] x86: Replace sse2 instructions with avx in memcmp-evex-movbe.S | expand |
On Fri, Oct 22, 2021 at 10:26 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote: > > This commit replaces two usages of SSE2 'movups' with AVX 'vmovdqu'. > > it could potentially be dangerous to use SSE2 if this function is ever > called without using 'vzeroupper' beforehand. While compilers appear > to use 'vzeroupper' before function calls if AVX2 has been used, using > SSE2 here is more brittle. Since it is not absolutely necessary it > should be avoided. > > It costs 2-extra bytes but the extra bytes should only eat into > alignment padding. > --- > sysdeps/x86_64/multiarch/memcmp-evex-movbe.S | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S b/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S > index 2761b54f2e..640f6757fa 100644 > --- a/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S > +++ b/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S > @@ -561,13 +561,13 @@ L(between_16_31): > /* From 16 to 31 bytes. No branch when size == 16. */ > > /* Use movups to save code size. */ > - movups (%rsi), %xmm2 > + vmovdqu (%rsi), %xmm2 > VPCMP $4, (%rdi), %xmm2, %k1 > kmovd %k1, %eax > testl %eax, %eax > jnz L(return_vec_0_lv) > /* Use overlapping loads to avoid branches. */ > - movups -16(%rsi, %rdx, CHAR_SIZE), %xmm2 > + vmovdqu -16(%rsi, %rdx, CHAR_SIZE), %xmm2 > VPCMP $4, -16(%rdi, %rdx, CHAR_SIZE), %xmm2, %k1 > addl $(CHAR_PER_VEC - (16 / CHAR_SIZE)), %edx > kmovd %k1, %eax > -- > 2.29.2 > LGTM. Reviewed-by: H.J. Lu <hjl.tools@gmail.com> Thanks.
On Sat, Oct 23, 2021 at 6:22 AM H.J. Lu via Libc-alpha <libc-alpha@sourceware.org> wrote: > > On Fri, Oct 22, 2021 at 10:26 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote: > > > > This commit replaces two usages of SSE2 'movups' with AVX 'vmovdqu'. > > > > it could potentially be dangerous to use SSE2 if this function is ever > > called without using 'vzeroupper' beforehand. While compilers appear > > to use 'vzeroupper' before function calls if AVX2 has been used, using > > SSE2 here is more brittle. Since it is not absolutely necessary it > > should be avoided. > > > > It costs 2-extra bytes but the extra bytes should only eat into > > alignment padding. > > --- > > sysdeps/x86_64/multiarch/memcmp-evex-movbe.S | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S b/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S > > index 2761b54f2e..640f6757fa 100644 > > --- a/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S > > +++ b/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S > > @@ -561,13 +561,13 @@ L(between_16_31): > > /* From 16 to 31 bytes. No branch when size == 16. */ > > > > /* Use movups to save code size. */ > > - movups (%rsi), %xmm2 > > + vmovdqu (%rsi), %xmm2 > > VPCMP $4, (%rdi), %xmm2, %k1 > > kmovd %k1, %eax > > testl %eax, %eax > > jnz L(return_vec_0_lv) > > /* Use overlapping loads to avoid branches. */ > > - movups -16(%rsi, %rdx, CHAR_SIZE), %xmm2 > > + vmovdqu -16(%rsi, %rdx, CHAR_SIZE), %xmm2 > > VPCMP $4, -16(%rdi, %rdx, CHAR_SIZE), %xmm2, %k1 > > addl $(CHAR_PER_VEC - (16 / CHAR_SIZE)), %edx > > kmovd %k1, %eax > > -- > > 2.29.2 > > > > LGTM. > > Reviewed-by: H.J. Lu <hjl.tools@gmail.com> > > Thanks. > > -- > H.J. I would like to backport this patch to release branches. Any comments or objections? --Sunil
diff --git a/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S b/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S index 2761b54f2e..640f6757fa 100644 --- a/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S +++ b/sysdeps/x86_64/multiarch/memcmp-evex-movbe.S @@ -561,13 +561,13 @@ L(between_16_31): /* From 16 to 31 bytes. No branch when size == 16. */ /* Use movups to save code size. */ - movups (%rsi), %xmm2 + vmovdqu (%rsi), %xmm2 VPCMP $4, (%rdi), %xmm2, %k1 kmovd %k1, %eax testl %eax, %eax jnz L(return_vec_0_lv) /* Use overlapping loads to avoid branches. */ - movups -16(%rsi, %rdx, CHAR_SIZE), %xmm2 + vmovdqu -16(%rsi, %rdx, CHAR_SIZE), %xmm2 VPCMP $4, -16(%rdi, %rdx, CHAR_SIZE), %xmm2, %k1 addl $(CHAR_PER_VEC - (16 / CHAR_SIZE)), %edx kmovd %k1, %eax