powerpc: Improve strcmp performance for shorter strings

For strings >16B and <32B existing algorithm takes more time than default
implementation when strings are placed closed to end of page. This is due
to byte by byte access for handling page cross. This is improved by
following >32B code path where the address is adjusted to aligned memory
before doing load doubleword operation instead of loading bytes.

Tested on powerpc64 and powerpc64le.

diff --git a/ChangeLog b/ChangeLog
index 6399c1f..769e738 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2017-02-07  Rajalakshmi Srinivasaraghavan  <raji@linux.vnet.ibm.com>
+
+       * sysdeps/powerpc/powerpc64/power8/strcmp.S: Adjust address for
+       unaligned load for shorter strings.
+       * sysdeps/powerpc/powerpc64/power9/strcmp.S: Likewise.
+
 2017-02-06  Joseph Myers  <joseph@codesourcery.com>
 
        * math/libm-test-driver.c (flag_test_errno): New variable.

diff --git a/sysdeps/powerpc/powerpc64/power8/strcmp.S b/sysdeps/powerpc/powerpc64/power8/strcmp.S
index c34ff4a..d46bff8 100644 (file)
--- a/sysdeps/powerpc/powerpc64/power8/strcmp.S
+++ b/sysdeps/powerpc/powerpc64/power8/strcmp.S
@@ -30,21 +30,21 @@
 EALIGN (strcmp, 4, 0)
        li      r0,0
 
-       /* Check if [s1]+32 or [s2]+32 will cross a 4K page boundary using
+       /* Check if [s1]+16 or [s2]+16 will cross a 4K page boundary using
           the code:
 
            (((size_t) s1) % PAGE_SIZE > (PAGE_SIZE - ITER_SIZE))
 
-          with PAGE_SIZE being 4096 and ITER_SIZE begin 32.  */
+          with PAGE_SIZE being 4096 and ITER_SIZE begin 16.  */
 
        rldicl  r7,r3,0,52
        rldicl  r9,r4,0,52
-       cmpldi  cr7,r7,4096-32
+       cmpldi  cr7,r7,4096-16
        bgt     cr7,L(pagecross_check)
-       cmpldi  cr5,r9,4096-32
+       cmpldi  cr5,r9,4096-16
        bgt     cr5,L(pagecross_check)
 
-       /* For short string up to 32 bytes, load both s1 and s2 using
+       /* For short string up to 16 bytes, load both s1 and s2 using
           unaligned dwords and compare.  */
        ld      r8,0(r3)
        ld      r10,0(r4)
@@ -60,25 +60,11 @@ EALIGN (strcmp, 4, 0)
        orc.    r9,r12,r11
        bne     cr0,L(different_nocmpb)
 
-       ld      r8,16(r3)
-       ld      r10,16(r4)
-       cmpb    r12,r8,r0
-       cmpb    r11,r8,r10
-       orc.    r9,r12,r11
-       bne     cr0,L(different_nocmpb)
-
-       ld      r8,24(r3)
-       ld      r10,24(r4)
-       cmpb    r12,r8,r0
-       cmpb    r11,r8,r10
-       orc.    r9,r12,r11
-       bne     cr0,L(different_nocmpb)
-
-       addi    r7,r3,32
-       addi    r4,r4,32
+       addi    r7,r3,16
+       addi    r4,r4,16
 
 L(align_8b):
-       /* Now it has checked for first 32 bytes, align source1 to doubleword
+       /* Now it has checked for first 16 bytes, align source1 to doubleword
           and adjust source2 address.  */
        rldicl  r9,r7,0,61      /* source1 alignment to doubleword  */
        subf    r4,r9,r4        /* Adjust source2 address based on source1

diff --git a/sysdeps/powerpc/powerpc64/power9/strcmp.S b/sysdeps/powerpc/powerpc64/power9/strcmp.S
index 3e32396..17ec8c2 100644 (file)
--- a/sysdeps/powerpc/powerpc64/power9/strcmp.S
+++ b/sysdeps/powerpc/powerpc64/power9/strcmp.S
@@ -65,21 +65,21 @@
 EALIGN (strcmp, 4, 0)
        li      r0, 0
 
-       /* Check if [s1]+32 or [s2]+32 will cross a 4K page boundary using
+       /* Check if [s1]+16 or [s2]+16 will cross a 4K page boundary using
           the code:
 
            (((size_t) s1) % PAGE_SIZE > (PAGE_SIZE - ITER_SIZE))
 
-          with PAGE_SIZE being 4096 and ITER_SIZE begin 32.  */
+          with PAGE_SIZE being 4096 and ITER_SIZE begin 16.  */
 
        rldicl  r7, r3, 0, 52
        rldicl  r9, r4, 0, 52
-       cmpldi  cr7, r7, 4096-32
+       cmpldi  cr7, r7, 4096-16
        bgt     cr7, L(pagecross_check)
-       cmpldi  cr5, r9, 4096-32
+       cmpldi  cr5, r9, 4096-16
        bgt     cr5, L(pagecross_check)
 
-       /* For short strings up to 32 bytes,  load both s1 and s2 using
+       /* For short strings up to 16 bytes,  load both s1 and s2 using
           unaligned dwords and compare.  */
        ld      r8, 0(r3)
        ld      r10, 0(r4)
@@ -95,25 +95,11 @@ EALIGN (strcmp, 4, 0)
        orc.    r9, r12, r11
        bne     cr0, L(different_nocmpb)
 
-       ld      r8, 16(r3)
-       ld      r10, 16(r4)
-       cmpb    r12, r8, r0
-       cmpb    r11, r8, r10
-       orc.    r9, r12, r11
-       bne     cr0, L(different_nocmpb)
-
-       ld      r8, 24(r3)
-       ld      r10, 24(r4)
-       cmpb    r12, r8, r0
-       cmpb    r11, r8, r10
-       orc.    r9, r12, r11
-       bne     cr0, L(different_nocmpb)
-
-       addi    r7, r3, 32
-       addi    r4, r4, 32
+       addi    r7, r3, 16
+       addi    r4, r4, 16
 
 L(align):
-       /* Now it has checked for first 32 bytes.  */
+       /* Now it has checked for first 16 bytes.  */
        vspltisb        v0, 0
        vspltisb        v2, -1
        lvsr    v6, 0, r4   /* Compute mask.  */