[PATCH v2] x86-64: Use 32-bit zero idiom for shorter encoding

[George Hu]

Replace the 64-bit zero idiom with the 32-bit form. In 64-bit mode,
zeroing the lower 32 bits of a GPR implicitly clears the entire
register. The 32-bit encoding is one byte shorter while preserving
identical semantics.
---
 sysdeps/mach/hurd/x86_64/static-start.S          | 2 +-
 sysdeps/mach/hurd/x86_64/tst-sig-redzone.c       | 2 +-
 sysdeps/x86_64/multiarch/strcat-sse2-unaligned.S | 2 +-
 sysdeps/x86_64/multiarch/strchr-sse2-no-bsf.S    | 2 +-
 sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S | 4 ++--
 sysdeps/x86_64/multiarch/strlen-sse2.S           | 2 +-
 sysdeps/x86_64/multiarch/wcschr-sse2.S           | 2 +-
 sysdeps/x86_64/multiarch/wcscmp-sse2.S           | 2 +-
 8 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/sysdeps/mach/hurd/x86_64/static-start.S b/sysdeps/mach/hurd/x86_64/static-start.S
index ec9c50239e..d670d45210 100644
--- a/sysdeps/mach/hurd/x86_64/static-start.S
+++ b/sysdeps/mach/hurd/x86_64/static-start.S
@@ -27,7 +27,7 @@ _start:
 
 	movq %rsp, %rdi
 	call _hurd_stack_setup
-	xorq %rdx, %rdx
+	xorl %edx, %edx
 	jmp _start1
 
 #define _start _start1
diff --git a/sysdeps/mach/hurd/x86_64/tst-sig-redzone.c b/sysdeps/mach/hurd/x86_64/tst-sig-redzone.c
index 32c7ab90f4..24b510c0aa 100644
--- a/sysdeps/mach/hurd/x86_64/tst-sig-redzone.c
+++ b/sysdeps/mach/hurd/x86_64/tst-sig-redzone.c
@@ -103,7 +103,7 @@ asm (
 "repe	scasq\n"
 "	jne	fail\n"
 
-"	xor	%rax,%rax\n"
+"	xor	%eax,%eax\n"
 "	ret\n"
 "fail:\n"
 "	movq	$1,%rax\n"
diff --git a/sysdeps/x86_64/multiarch/strcat-sse2-unaligned.S b/sysdeps/x86_64/multiarch/strcat-sse2-unaligned.S
index 1c04d611be..3c3f039047 100644
--- a/sysdeps/x86_64/multiarch/strcat-sse2-unaligned.S
+++ b/sysdeps/x86_64/multiarch/strcat-sse2-unaligned.S
@@ -45,7 +45,7 @@ ENTRY (STRCAT)
 /* Inline corresponding strlen file, temporary until new strcpy
    implementation gets merged.  */
 
-	xor	%rax, %rax
+	xor	%eax, %eax
 	mov	%edi, %ecx
 	and	$0x3f, %ecx
 	pxor	%xmm0, %xmm0
diff --git a/sysdeps/x86_64/multiarch/strchr-sse2-no-bsf.S b/sysdeps/x86_64/multiarch/strchr-sse2-no-bsf.S
index 9521cd4dc4..7d2677b4fd 100644
--- a/sysdeps/x86_64/multiarch/strchr-sse2-no-bsf.S
+++ b/sysdeps/x86_64/multiarch/strchr-sse2-no-bsf.S
@@ -69,7 +69,7 @@ L(loop):
 /* Return NULL.  */
 	.p2align 4
 L(return_null):
-	xor	%rax, %rax
+	xor	%eax, %eax
 	ret
 
 L(matches):
diff --git a/sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S b/sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S
index 3dfee3039a..59ff7bc85e 100644
--- a/sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S
+++ b/sysdeps/x86_64/multiarch/strcpy-sse2-unaligned.S
@@ -1657,7 +1657,7 @@ L(CopyFrom1To16BytesXmmExit):
 	.p2align 4
 L(StrncpyFillTailWithZero):
 	pxor	%xmm0, %xmm0
-	xor	%rdx, %rdx
+	xor	%edx, %edx
 	sub	$16, %r8
 	jbe	L(StrncpyFillExit)
 
@@ -1736,7 +1736,7 @@ L(Unaligned64LeaveCase3):
 
 	.p2align 4
 L(Unaligned64LeaveCase2):
-	xor	%rcx, %rcx
+	xor	%ecx, %ecx
 	pcmpeqb	%xmm4, %xmm0
 	pmovmskb %xmm0, %rdx
 	add	$48, %r8
diff --git a/sysdeps/x86_64/multiarch/strlen-sse2.S b/sysdeps/x86_64/multiarch/strlen-sse2.S
index ca6e0812be..6085ad1236 100644
--- a/sysdeps/x86_64/multiarch/strlen-sse2.S
+++ b/sysdeps/x86_64/multiarch/strlen-sse2.S
@@ -77,7 +77,7 @@ ENTRY(STRLEN)
 /* Do not read anything when n==0.  */
 	test	%RSI_LP, %RSI_LP
 	jne	L(n_nonzero)
-	xor	%rax, %rax
+	xor	%eax, %eax
 	ret
 L(n_nonzero):
 #  ifdef AS_WCSLEN
diff --git a/sysdeps/x86_64/multiarch/wcschr-sse2.S b/sysdeps/x86_64/multiarch/wcschr-sse2.S
index ec11a16a73..f0069f026a 100644
--- a/sysdeps/x86_64/multiarch/wcschr-sse2.S
+++ b/sysdeps/x86_64/multiarch/wcschr-sse2.S
@@ -155,7 +155,7 @@ L(match):
 
 	.p2align 4
 L(return_null):
-	xor	%rax, %rax
+	xor	%eax, %eax
 	ret
 
 END (WCSCHR)
diff --git a/sysdeps/x86_64/multiarch/wcscmp-sse2.S b/sysdeps/x86_64/multiarch/wcscmp-sse2.S
index 5ab124e0a7..a54615a9ae 100644
--- a/sysdeps/x86_64/multiarch/wcscmp-sse2.S
+++ b/sysdeps/x86_64/multiarch/wcscmp-sse2.S
@@ -950,7 +950,7 @@ L(nequal_bigger):
 
 	.p2align 4
 L(equal):
-	xor	%rax, %rax
+	xor	%eax, %eax
 	ret
 
 END (STRCMP)
-- 
2.52.0