PATCH: powerpc/strchr.S for BPs

[Greg McGary]

This patch undoes Franz's temporary fix and introduces a permanent fix
that will work for BP and non-BP.  It passes string/tester.

I changed the way strchr returns NULL:

Before:	We zeroed the return-value register, then in two places
	conditionally branched to LR.

After:	In two places, we conditionally branch to a label that
	zeroes the return-value register then unconditionally branches
	to LR.

This adds one insn overall to the size.
It adds one extra unconditional branch to the return-NULL case.
It saves a register move for the return-non-NULL case.

IMO, it's a basically wash.

The primary virtue of this approach is that it avoids all #ifs
on __BOUNDED_POINTERS__ enhancing maintainability.

What follows immediately for review is a patch relative to the
previous version (before Franz's temporary fix), so as to not obscure
the meaningful parts with the reversal of the temporary fix.  (The
complete patch is at the end.)

OK?

Greg

Index: sysdeps/powerpc/strchr.S
===================================================================
RCS file: /cvs/glibc/libc/sysdeps/powerpc/strchr.S,v
retrieving revision 1.4
diff -u -p -B -w -r1.4 strchr.S
--- strchr.S	2000/07/04 00:24:42	1.4
+++ strchr.S	2000/07/22 08:34:22
@@ -88,11 +89,9 @@ L(loopentry):
    before or after the zero byte).  In fact, we may be looking for a
    zero byte, in which case we return a match.  We guess that this hasn't
    happened, though.  */
-L(missed):
 	and.	rTMP1, rTMP1, rTMP2
-	li	rSTR, 0
-	STORE_RETURN_VALUE (rSTR)
-	beqlr
+	beq	L(return_NULL)
+
 /* It did happen. Decide which one was first...
    I'm not sure if this is actually faster than a sequence of
    rotates, compares, and branches (we use it anyway because it's shorter).  */
@@ -105,7 +104,8 @@ L(missed):
 	nor	rWORD, rMASK, rFEFE
 	nor	rTMP2, rIGN, rTMP1
 	cmplw	rWORD, rTMP2
-	bgtlr
+	bgt	L(return_NULL)
+
 	cntlzw	rCLZB, rTMP2
 	srwi	rCLZB, rCLZB, 3
 	add	rSTR, rSTR, rCLZB
@@ -113,6 +113,7 @@ L(missed):
 	STORE_RETURN_VALUE (rSTR)
 	blr
 
+/* We found a CHR byte in WORD, and there is no 00 byte present in WORD.  */
 L(foundit):
 	and	rTMP1, r7F7F, rTMP3
 	or	rIGN, r7F7F, rTMP3
@@ -125,6 +126,12 @@ L(foundit):
 	CHECK_BOUNDS_HIGH_RTN (rSTR, rTMP2, twlge)
 	STORE_RETURN_VALUE (rSTR)
 	blr
+
+L(return_NULL):
+	li	rSTR, 0
+	STORE_RETURN_VALUE (rSTR)
+	blr
+
 END (BP_SYM (strchr))
 
 weak_alias (BP_SYM (strchr), BP_SYM (index))
------------------------------------------------------------------------------

This is the complete patch that includes backing out the temporary
fix.

Index: sysdeps/powerpc/strchr.S
===================================================================
RCS file: /cvs/glibc/libc/sysdeps/powerpc/strchr.S,v
retrieving revision 1.5
diff -u -p -B -w -r1.5 strchr.S
--- strchr.S	2000/07/22 02:25:05	1.5
+++ strchr.S	2000/07/22 08:34:50
@@ -34,7 +34,7 @@ ENTRY (BP_SYM (strchr))
 # define rCHR	r5	/* byte we're looking for, spread over the whole word */
 # define rWORD	r8	/* the current word */
 #else
-# define rSTR	r8	/* current word pointer */
+# define rSTR	r3	/* current word pointer */
 # define rCHR	r4	/* byte we're looking for, spread over the whole word */
 # define rWORD	r5	/* the current word */
 #endif
@@ -52,10 +52,10 @@ ENTRY (BP_SYM (strchr))
 	rlwimi	rCHR, rCHR, 8, 16, 23
 	li	rMASK, -1
 	rlwimi	rCHR, rCHR, 16, 0, 15
-	rlwinm	rIGN, rRTN, 3, 27, 28
+	rlwinm	rIGN, rSTR, 3, 27, 28
 	lis	rFEFE, -0x101
 	lis	r7F7F, 0x7f7f
-	clrrwi	rSTR, rRTN, 2
+	clrrwi	rSTR, rSTR, 2
 	addi	rFEFE, rFEFE, -0x101
 	addi	r7F7F, r7F7F, 0x7f7f
 /* Test the first (partial?) word.  */
@@ -88,11 +89,9 @@ L(loopentry):
    before or after the zero byte).  In fact, we may be looking for a
    zero byte, in which case we return a match.  We guess that this hasn't
    happened, though.  */
-L(missed):
 	and.	rTMP1, rTMP1, rTMP2
-	li	rRTN, 0
-	STORE_RETURN_VALUE (rSTR)
-	beqlr
+	beq	L(return_NULL)
+
 /* It did happen. Decide which one was first...
    I'm not sure if this is actually faster than a sequence of
    rotates, compares, and branches (we use it anyway because it's shorter).  */
@@ -105,14 +104,16 @@ L(missed):
 	nor	rWORD, rMASK, rFEFE
 	nor	rTMP2, rIGN, rTMP1
 	cmplw	rWORD, rTMP2
-	bgtlr
+	bgt	L(return_NULL)
+
 	cntlzw	rCLZB, rTMP2
 	srwi	rCLZB, rCLZB, 3
-	add	rRTN, rSTR, rCLZB
+	add	rSTR, rSTR, rCLZB
 	CHECK_BOUNDS_HIGH_RTN (rSTR, rTMP2, twlge)
 	STORE_RETURN_VALUE (rSTR)
 	blr
 
+/* We found a CHR byte in WORD, and there is no 00 byte present in WORD.  */
 L(foundit):
 	and	rTMP1, r7F7F, rTMP3
 	or	rIGN, r7F7F, rTMP3
@@ -121,10 +122,16 @@ L(foundit):
 	cntlzw	rCLZB, rTMP2
 	subi	rSTR, rSTR, 4
 	srwi	rCLZB, rCLZB, 3
-	add	rRTN, rSTR, rCLZB
+	add	rSTR, rSTR, rCLZB
 	CHECK_BOUNDS_HIGH_RTN (rSTR, rTMP2, twlge)
 	STORE_RETURN_VALUE (rSTR)
 	blr
+
+L(return_NULL):
+	li	rSTR, 0
+	STORE_RETURN_VALUE (rSTR)
+	blr
+
 END (BP_SYM (strchr))
 
 weak_alias (BP_SYM (strchr), BP_SYM (index))