powerpc: optimize strcpy/stpcpy for POWER9/10

This patch modifies the current POWER9 implementation of strcpy and
stpcpy to optimize it for POWER9/10.

Since no new POWER10 instructions are used, the original POWER9 strcpy is
modified instead of creating a new implementation for POWER10.  This
implementation is based on both the original POWER9 implementation of
strcpy and the preamble of the new POWER10 implementation of strlen.

The changes also affect stpcpy, which uses the same implementation with
some additional code before returning.

On POWER9, averaging improvements across the benchmark
inputs (length/source alignment/destination alignment), for an
experiment that ran the benchmark five times, bench-strcpy showed an
improvement of 5.23%, and bench-stpcpy showed an improvement of 6.59%.

On POWER10, bench-strcpy showed 13.16%, and bench-stpcpy showed 13.59%.

The changes are:

1. Removed the null string optimization.

   Although this results in a few extra cycles for the null string, in
   combination with the second change, this resulted in improvements for
   for other cases.

2. Adapted the preamble from strlen for POWER10.

   This is the part of the function that handles up to the first 16 bytes
   of the string.

3. Increased number of unrolled iterations in the main loop to 6.

Reviewed-by: Matheus Castanho <msc@linux.ibm.com>
Tested-by: Matheus Castanho <msc@linux.ibm.com>

diff --git a/sysdeps/powerpc/powerpc64/le/power9/strcpy.S b/sysdeps/powerpc/powerpc64/le/power9/strcpy.S
index 76cfcae..b9e5afd 100644 (file)
--- a/sysdeps/powerpc/powerpc64/le/power9/strcpy.S
+++ b/sysdeps/powerpc/powerpc64/le/power9/strcpy.S
@@ -45,91 +45,78 @@
    The implementation can load bytes past a null terminator, but only
    up to the next 16B boundary, so it never crosses a page.  */
 
+/* Load quadword at addr+offset to vreg, check for null bytes,
+   and branch to label if any are found.  */
+#define CHECK16(vreg,offset,addr,label) \
+       lxv     vreg+32,offset(addr);   \
+       vcmpequb. v6,vreg,v18;  \
+       bne     cr6,L(label);
+
 .machine power9
 ENTRY_TOCLESS (FUNC_NAME, 4)
        CALL_MCOUNT 2
 
-       /* NULL string optimisation  */
-       lbz     r0,0(r4)
-       stb     r0,0(r3)
-       cmpwi   r0,0
-       beqlr
-
-       addi    r4,r4,1
-       addi    r11,r3,1
-
        vspltisb v18,0          /* Zeroes in v18  */
+       vspltisb v19,-1         /* 0xFF bytes in v19  */
 
-       neg     r5,r4
-       rldicl  r9,r5,0,60      /* How many bytes to get source 16B aligned?  */
+       /* Next 16B-aligned address. Prepare address for L(loop).  */
+       addi    r5,r4,16
+       clrrdi  r5,r5,4
+       subf    r8,r4,r5
+       add     r11,r3,r8
 
-       /* Get source 16B aligned  */
+       /* Align data and fill bytes not loaded with non matching char.  */
        lvx     v0,0,r4
        lvsr    v1,0,r4
-       vperm   v0,v18,v0,v1
-
-       vcmpequb v6,v0,v18      /* 0xff if byte is NULL, 0x00 otherwise  */
-       vctzlsbb r7,v6          /* Number of trailing zeroes  */
-       addi    r8,r7,1         /* Add null terminator  */
+       vperm   v0,v19,v0,v1
 
-       /* r8 = bytes including null
-          r9 = bytes to get source 16B aligned
-          if r8 > r9
-             no null, copy r9 bytes
-          else
-             there is a null, copy r8 bytes and return.  */
-       cmpd    r8,r9
-       bgt     L(no_null)
+       vcmpequb. v6,v0,v18     /* 0xff if byte is NULL, 0x00 otherwise  */
+       beq     cr6,L(no_null)
 
-       sldi    r10,r8,56       /* stxvl wants size in top 8 bits  */
-       stxvl   32+v0,r11,r10   /* Partial store  */
+       /* There's a null byte.  */
+       vctzlsbb r8,v6          /* Number of trailing zeroes  */
+       addi    r9,r8,1         /* Add null byte.  */
+       sldi    r10,r9,56       /* stxvl wants size in top 8 bits.  */
+       stxvl   32+v0,r3,r10    /* Partial store  */
 
 #ifdef USE_AS_STPCPY
        /* stpcpy returns the dest address plus the size not counting the
           final '\0'.  */
-       add     r3,r11,r7
+       add     r3,r3,r8
 #endif
        blr
 
 L(no_null):
-       sldi    r10,r9,56       /* stxvl wants size in top 8 bits  */
-       stxvl   32+v0,r11,r10   /* Partial store  */
-
-       add     r4,r4,r9
-       add     r11,r11,r9
+       sldi    r10,r8,56       /* stxvl wants size in top 8 bits  */
+       stxvl   32+v0,r3,r10    /* Partial store  */
 
+       .p2align 4
 L(loop):
-       lxv     32+v0,0(r4)
-       vcmpequb. v6,v0,v18     /* Any zero bytes?  */
-       bne     cr6,L(tail1)
-
-       lxv     32+v1,16(r4)
-       vcmpequb. v6,v1,v18     /* Any zero bytes?  */
-       bne     cr6,L(tail2)
-
-       lxv     32+v2,32(r4)
-       vcmpequb. v6,v2,v18     /* Any zero bytes?  */
-       bne     cr6,L(tail3)
-
-       lxv     32+v3,48(r4)
-       vcmpequb. v6,v3,v18     /* Any zero bytes?  */
-       bne     cr6,L(tail4)
+       CHECK16(v0,0,r5,tail1)
+       CHECK16(v1,16,r5,tail2)
+       CHECK16(v2,32,r5,tail3)
+       CHECK16(v3,48,r5,tail4)
+       CHECK16(v4,64,r5,tail5)
+       CHECK16(v5,80,r5,tail6)
 
        stxv    32+v0,0(r11)
        stxv    32+v1,16(r11)
        stxv    32+v2,32(r11)
        stxv    32+v3,48(r11)
+       stxv    32+v4,64(r11)
+       stxv    32+v5,80(r11)
 
-       addi    r4,r4,64
-       addi    r11,r11,64
+       addi    r5,r5,96
+       addi    r11,r11,96
 
        b       L(loop)
 
+       .p2align 4
 L(tail1):
-       vctzlsbb r8,v6
-       addi    r9,r8,1
+       vctzlsbb r8,v6          /* Number of trailing zeroes  */
+       addi    r9,r8,1         /* Add null terminator  */
        sldi    r9,r9,56        /* stxvl wants size in top 8 bits  */
-       stxvl   32+v0,r11,r9
+       stxvl   32+v0,r11,r9    /* Partial store  */
 #ifdef USE_AS_STPCPY
        /* stpcpy returns the dest address plus the size not counting the
           final '\0'.  */
@@ -137,50 +124,81 @@ L(tail1):
 #endif
        blr
 
+       .p2align 4
 L(tail2):
        stxv    32+v0,0(r11)
-       vctzlsbb r8,v6          /* Number of trailing zeroes  */
-       addi    r9,r8,1         /* Add null terminator  */
-       sldi    r10,r9,56       /* stxvl wants size in top 8 bits  */
+       vctzlsbb r8,v6
+       addi    r9,r8,1
+       sldi    r9,r9,56
        addi    r11,r11,16
-       stxvl   32+v1,r11,r10   /* Partial store  */
+       stxvl   32+v1,r11,r9
 #ifdef USE_AS_STPCPY
-       /* stpcpy returns the dest address plus the size not counting the
-          final '\0'.  */
        add     r3,r11,r8
 #endif
        blr
 
+       .p2align 4
 L(tail3):
        stxv    32+v0,0(r11)
        stxv    32+v1,16(r11)
-       vctzlsbb r8,v6          /* Number of trailing zeroes  */
-       addi    r9,r8,1         /* Add null terminator  */
-       sldi    r10,r9,56       /* stxvl wants size in top 8 bits  */
+       vctzlsbb r8,v6
+       addi    r9,r8,1
+       sldi    r9,r9,56
        addi    r11,r11,32
-       stxvl   32+v2,r11,r10   /* Partial store  */
+       stxvl   32+v2,r11,r9
 #ifdef USE_AS_STPCPY
-       /* stpcpy returns the dest address plus the size not counting the
-          final '\0'.  */
        add     r3,r11,r8
 #endif
        blr
 
+       .p2align 4
 L(tail4):
        stxv    32+v0,0(r11)
        stxv    32+v1,16(r11)
        stxv    32+v2,32(r11)
-       vctzlsbb r8,v6          /* Number of trailing zeroes  */
-       addi    r9,r8,1         /* Add null terminator  */
-       sldi    r10,r9,56       /* stxvl wants size in top 8 bits  */
+       vctzlsbb r8,v6
+       addi    r9,r8,1
+       sldi    r9,r9,56
        addi    r11,r11,48
-       stxvl   32+v3,r11,r10   /* Partial store  */
+       stxvl   32+v3,r11,r9
 #ifdef USE_AS_STPCPY
-       /* stpcpy returns the dest address plus the size not counting the
-          final '\0'.  */
        add     r3,r11,r8
 #endif
        blr
+
+       .p2align 4
+L(tail5):
+       stxv    32+v0,0(r11)
+       stxv    32+v1,16(r11)
+       stxv    32+v2,32(r11)
+       stxv    32+v3,48(r11)
+       vctzlsbb r8,v6
+       addi    r9,r8,1
+       sldi    r9,r9,56
+       addi    r11,r11,64
+       stxvl   32+v4,r11,r9
+#ifdef USE_AS_STPCPY
+       add     r3,r11,r8
+#endif
+       blr
+
+       .p2align 4
+L(tail6):
+       stxv    32+v0,0(r11)
+       stxv    32+v1,16(r11)
+       stxv    32+v2,32(r11)
+       stxv    32+v3,48(r11)
+       stxv    32+v4,64(r11)
+       vctzlsbb r8,v6
+       addi    r9,r8,1
+       sldi    r9,r9,56
+       addi    r11,r11,80
+       stxvl   32+v5,r11,r9
+#ifdef USE_AS_STPCPY
+       add     r3,r11,r8
+#endif
+       blr
+
 END (FUNC_NAME)
 #ifndef USE_AS_STPCPY
 libc_hidden_builtin_def (strcpy)