powerpc: Handle worstcase behavior in strstr() for POWER7

Instead of checking needle length, constant 'n' number of comparisons
is checked to fall back to default implementation.  This patch is tested
on powerpc64 and powerpc64le.

2015-08-25  Rajalakshmi Srinivasaraghavan  <raji@linux.vnet.ibm.com>

	* sysdeps/powerpc/powerpc64/power7/strstr.S: Handle worst case.

ChangeLog

@@ -1,3 +1,7 @@
+2015-08-25  Rajalakshmi Srinivasaraghavan  <raji@linux.vnet.ibm.com>
+
+	* sysdeps/powerpc/powerpc64/power7/strstr.S: Handle worst case.
+
 2015-08-25  H.J. Lu  <hongjiu.lu@intel.com>
 
 	* sysdeps/x86_64/strlen.S: Replace %xmm[8-12] with %xmm[0-4].

sysdeps/powerpc/powerpc64/power7/strstr.S

@@ -23,6 +23,8 @@
 /* The performance gain is obtained using aligned memory access, load
  * doubleword and usage of cmpb instruction for quicker comparison.  */
 
+#define ITERATIONS	64
+
 #ifndef STRLEN
 /* For builds with no IFUNC support, local calls should be made to internal
    GLIBC symbol (created by libc_hidden_builtin_def).  */
@@ -62,14 +64,15 @@ EALIGN (strstr, 4, 0)
 	cfi_offset(r30, -16)
 	std	r29, -24(r1)		/* Save callers register r29.  */
 	cfi_offset(r29, -24)
+	std	r28, -32(r1)		/* Save callers register r28.  */
+	cfi_offset(r28, -32)
 	std	r0, 16(r1)		/* Store the link register.  */
 	cfi_offset(lr, 16)
 	stdu	r1, -FRAMESIZE(r1)	/* Create the stack frame.  */
 	cfi_adjust_cfa_offset(FRAMESIZE)
 
 	dcbt	0, r3
 	dcbt	0, r4
-
 	cmpdi	cr7, r3, 0
 	beq	cr7, L(retnull)
 	cmpdi	cr7, r4, 0
@@ -84,10 +87,6 @@ EALIGN (strstr, 4, 0)
 	cmpdi	cr7, r3, 0	/* If search str is null.  */
 	beq	cr7, L(ret_r3)
 
-	/* Call __strstr_ppc if needle len > 2048 */
-	cmpdi	cr7, r3, 2048
-	bgt	cr7, L(default)
-
 	mr	r31, r3
 	mr	r4, r3
 	mr	r3, r29
@@ -105,7 +104,8 @@ EALIGN (strstr, 4, 0)
 	/* If first char of search str is not present.  */
 	cmpdi	cr7, r3, 0
 	ble	cr7, L(end)
-
+	/* Reg r28 is used to count the number of iterations. */
+	li	r28, 0
 	rldicl	r8, r3, 0, 52	/* Page cross check.  */
 	cmpldi	cr7, r8, 4096-16
 	bgt	cr7, L(bytebybyte)
@@ -324,6 +324,10 @@ L(return4):
 	.align	4
 L(begin):
 	mr	r3, r8
+	/* When our iterations exceed ITERATIONS,fall back to default. */
+	addi	r28, r28, 1
+	cmpdi	cr7, r28, ITERATIONS
+	beq	cr7, L(default)
 	lbz	r4, 0(r30)
 	bl	STRCHR
 	nop
@@ -423,6 +427,10 @@ L(nextbyte):
 	cmpdi	cr7, r9, -1
 	beq	cr7, L(end)
 	addi	r3, r4, 1
+	/* When our iterations exceed ITERATIONS,fall back to default. */
+	addi	r28, r28, 1
+	cmpdi	cr7, r28, ITERATIONS
+	beq	cr7, L(default)
 	lbz	r4, 0(r30)
 	bl	STRCHR
 	nop
@@ -490,7 +498,6 @@ L(retnull):
 
 	.align	4
 L(default):
-	mr	r3, r29
 	mr	r4, r30
 	bl	__strstr_ppc
 	nop
@@ -500,6 +507,7 @@ L(end):
 	addi	r1, r1, FRAMESIZE	/* Restore stack pointer.  */
 	cfi_adjust_cfa_offset(-FRAMESIZE)
 	ld	r0, 16(r1)	/* Restore the saved link register.  */
+	ld	r28, -32(r1)	/* Restore callers save register r28.  */
 	ld	r29, -24(r1)	/* Restore callers save register r29.  */
 	ld	r30, -16(r1)	/* Restore callers save register r30.  */
 	ld	r31, -8(r1)	/* Restore callers save register r31.  */