powerpc: Zero pad using memset in strncpy/stpncpy

Call __memset_power8 to pad, with zeros, the remaining bytes in the
dest string on __strncpy_power8 and __stpncpy_power8.  This improves
performance when n is larger than the input string, giving ~30% gain for
larger strings without impacting much shorter strings.

diff --git a/ChangeLog b/ChangeLog
index 768c0a0d02f4e23b3ba36ea39bd4800cfbbffc3b..5f8424a08866a62b66b96ae428eb089646cf3dd2 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2016-04-29  Gabriel F. T. Gomes  <gftg@linux.vnet.ibm.com>
+
+       * sysdeps/powerpc/powerpc64/power8/strncpy.S: Call memset to pad the
+       remaining bytes in the dest string, with zeros.
+
 2016-04-29  Florian Weimer  <fweimer@redhat.com>
 
        [BZ #20010]

diff --git a/sysdeps/powerpc/powerpc64/power8/strncpy.S b/sysdeps/powerpc/powerpc64/power8/strncpy.S
index 17c3afb5fead869e03ab38fb6a671298fc618c74..0bb3bd46d71c187e374ea18992e55c908a1b5fee 100644 (file)
--- a/sysdeps/powerpc/powerpc64/power8/strncpy.S
+++ b/sysdeps/powerpc/powerpc64/power8/strncpy.S
@@ -24,6 +24,8 @@
 # define FUNC_NAME strncpy
 #endif
 
+#define FRAMESIZE (FRAME_MIN_SIZE+48)
+
 /* Implements the function
 
    char * [r3] strncpy (char *dest [r3], const char *src [r4], size_t n [r5])
@@ -54,8 +56,7 @@ EALIGN (FUNC_NAME, 4, 0)
        addi    r10,r4,16
        rlwinm  r9,r4,0,19,19
 
-       /* Since it is a leaf function, save some non-volatile registers on the
-          protected/red zone.  */
+       /* Save some non-volatile registers on the stack.  */
        std     r26,-48(r1)
        std     r27,-40(r1)
 
@@ -69,6 +70,14 @@ EALIGN (FUNC_NAME, 4, 0)
        std     r30,-16(r1)
        std     r31,-8(r1)
 
+       /* Update CFI.  */
+       cfi_offset(r26, -48)
+       cfi_offset(r27, -40)
+       cfi_offset(r28, -32)
+       cfi_offset(r29, -24)
+       cfi_offset(r30, -16)
+       cfi_offset(r31, -8)
+
        beq     cr7,L(unaligned_lt_16)
        rldicl  r9,r4,0,61
        subfic  r8,r9,8
@@ -180,74 +189,58 @@ L(short_path_loop_end):
        ld      r31,-8(r1)
        blr
 
-       /* This code pads the remainder dest with NULL bytes.  The algorithm
-          calculate the remanining size and issues a doubleword unrolled
-          loops followed by a byte a byte set.  */
+       /* This code pads the remainder of dest with NULL bytes.  The algorithm
+          calculates the remaining size and calls memset.  */
        .align  4
 L(zero_pad_start):
        mr      r5,r10
        mr      r9,r6
 L(zero_pad_start_1):
-       srdi.   r8,r5,r3
-       mr      r10,r9
-#ifdef USE_AS_STPNCPY
-       mr      r3,r9
+       /* At this point:
+            - r5 holds the number of bytes that still have to be written to
+              dest.
+            - r9 points to the position, in dest, where the first null byte
+              will be written.
+          The above statements are true both when control reaches this label
+          from a branch or when falling through the previous lines.  */
+#ifndef USE_AS_STPNCPY
+       mr      r30,r3       /* Save the return value of strncpy.  */
+#endif
+       /* Prepare the call to memset.  */
+       mr      r3,r9        /* Pointer to the area to be zero-filled.  */
+       li      r4,0         /* Byte to be written (zero).  */
+
+       /* We delayed the creation of the stack frame, as well as the saving of
+          the link register, because only at this point, we are sure that
+          doing so is actually needed.  */
+
+       /* Save the link register.  */
+       mflr    r0
+       std     r0,16(r1)
+       cfi_offset(lr, 16)
+
+       /* Create the stack frame.  */
+       stdu    r1,-FRAMESIZE(r1)
+       cfi_adjust_cfa_offset(FRAMESIZE)
+
+       bl      __memset_power8
+       nop
+
+       /* Restore the stack frame.  */
+       addi    r1,r1,FRAMESIZE
+       cfi_adjust_cfa_offset(-FRAMESIZE)
+       /* Restore the link register.  */
+       ld      r0,16(r1)
+       mtlr    r0
+
+#ifndef USE_AS_STPNCPY
+       mr      r3,r30       /* Restore the return value of strncpy, i.e.:
+                               dest.  For stpncpy, the return value is the
+                               same as return value of memset.  */
 #endif
-       beq-    cr0,L(zero_pad_loop_b_start)
-       cmpldi  cr7,r8,1
-       li      cr7,0
-       std     r7,0(r9)
-       beq     cr7,L(zero_pad_loop_b_prepare)
-       addic.  r8,r8,-2
-       addi    r10,r9,r16
-       std     r7,8(r9)
-       beq     cr0,L(zero_pad_loop_dw_2)
-       std     r7,16(r9)
-       li      r9,0
-       b       L(zero_pad_loop_dw_1)
-
-       .align  4
-L(zero_pad_loop_dw):
-       addi    r10,r10,16
-       std     r9,-8(r10)
-       beq     cr0,L(zero_pad_loop_dw_2)
-       std     r9,0(r10)
-L(zero_pad_loop_dw_1):
-       cmpldi  cr7,r8,1
-       std     r9,0(r10)
-       addic.  r8,r8,-2
-       bne     cr7,L(zero_pad_loop_dw)
-       addi    r10,r10,8
-L(zero_pad_loop_dw_2):
-       rldicl  r5,r5,0,61
-L(zero_pad_loop_b_start):
-       cmpdi   cr7,r5,0
-       addi    r5,r5,-1
-       addi    r9,r10,-1
-       add     r10,r10,5
-       subf    r10,r9,r10
-       li      r8,0
-       beq-    cr7,L(short_path_loop_end)
-
-       /* Write remaining 1-8 bytes.  */
-        .align  4
-       addi    r9,r9,1
-       mtocrf  0x1,r10
-       bf      29,4f
-        stw     r8,0(r9)
-        addi   r9,r9,4
-
-        .align  4
-4:      bf      30,2f
-        sth     r8,0(r9)
-        addi   r9,r9,2
-
-        .align  4
-2:      bf     31,1f
-        stb    r8,0(r9)
 
-       /* Restore non-volatile registers.  */
-1:     ld      r26,-48(r1)
+       /* Restore non-volatile registers and return.  */
+       ld      r26,-48(r1)
        ld      r27,-40(r1)
        ld      r28,-32(r1)
        ld      r29,-24(r1)
@@ -443,10 +436,6 @@ L(short_path_prepare_2_3):
        mr      r4,r28
        mr      r9,r29
        b       L(short_path_2)
-L(zero_pad_loop_b_prepare):
-       addi    r10,r9,8
-       rldicl  r5,r5,0,61
-       b       L(zero_pad_loop_b_start)
 L(zero_pad_start_prepare_1):
        mr      r5,r6
        mr      r9,r8