Hi,
Please find below a patch that optimizes libgcc routines for the RL78 target.

This is similar to my earlier patch submitted here,
https://gcc.gnu.org/ml/gcc-patches/2016-02/msg00415.html

The patch optimizes the loading of immediate value in the case of 0x00, by using the clrw or clrb instruction.
The patch replaces movw/mov instruction with the smaller clrw/clrb instruction.
The clrw and clrb generates only 1 byte of opcode as compared to 3 or 2 bytes for movw and mov.

Kindly review this patch and let me know what you think.
This is regression tested for rl78 -msim.

Best Regards,
Kaushik

p.s. Kindly ignore any disclaimers at end of this e-mail as they are auto-inserted.
Apologies for the same.

2016-04-06  Kaushik Phatak <kaushik.phatak@kpit.com>

	* config/rl78/bit-count.S: Use clrw/clrb where possible.
	* config/rl78/cmpsi2.S: Likewise.
	* config/rl78/divmodhi.S Likewise.
	* config/rl78/divmodsi.S Likewise.
	* config/rl78/fpbit-sf.S Likewise.
	* config/rl78/fpmath-sf.S Likewise.
	* config/rl78/mulsi3.S Likewise.

Index: libgcc/config/rl78/bit-count.S
===================================================================
--- libgcc/config/rl78/bit-count.S	(revision 3174)
+++ libgcc/config/rl78/bit-count.S	(working copy)
@@ -139,7 +139,7 @@
 	xor1	cy, a.5
 	xor1	cy, a.6
 	xor1	cy, a.7
-	movw	ax, #0
+	clrw	ax
 	bnc	$1f
 	incw	ax
 1:
@@ -190,7 +190,7 @@
 	movw	ax, sp
 	addw	ax, #4
 	movw	hl, ax
-	mov	a, #0
+	clrb	a
 1:
 	xch	a, b
 	mov	a, [hl]
@@ -207,7 +207,7 @@
 	bnz	$1b
 
 	mov	x, a
-	mov	a, #0
+	clrb	a
 	movw	r8, ax
 	ret	
 END_FUNC	___popcountqi_internal
Index: libgcc/config/rl78/cmpsi2.S
===================================================================
--- libgcc/config/rl78/cmpsi2.S	(revision 3174)
+++ libgcc/config/rl78/cmpsi2.S	(working copy)
@@ -162,8 +162,8 @@
 
 	;; They differ.  Subtract *S2 from *S1 and return as the result.
 	mov	x, a
-	mov	a, #0
-	mov	r9, #0
+	clrb	a
+	clrb	r9
 	subw	ax, r8
 1:
 	movw	r8, ax
Index: libgcc/config/rl78/divmodhi.S
===================================================================
--- libgcc/config/rl78/divmodhi.S	(revision 3174)
+++ libgcc/config/rl78/divmodhi.S	(working copy)
@@ -576,7 +576,7 @@
 
 .macro NEG_AX
 	movw	hl, ax
-	movw	ax, #0
+	clrw	ax
 	subw	ax, [hl]
 	movw	[hl], ax
 .endm
Index: libgcc/config/rl78/divmodsi.S
===================================================================
--- libgcc/config/rl78/divmodsi.S	(revision 3174)
+++ libgcc/config/rl78/divmodsi.S	(working copy)
@@ -952,10 +952,10 @@
 
 .macro NEG_AX
 	movw	hl, ax
-	movw	ax, #0
+	clrw	ax
 	subw	ax, [hl]
 	movw	[hl], ax
-	movw	ax, #0
+	clrw	ax
 	sknc
 	decw	ax
 	subw	ax, [hl+2]
Index: libgcc/config/rl78/fpbit-sf.S
===================================================================
--- libgcc/config/rl78/fpbit-sf.S	(revision 3174)
+++ libgcc/config/rl78/fpbit-sf.S	(working copy)
@@ -117,7 +117,7 @@
 	call	$!__int_iszero
 	bnz	$2f
 	;; At this point, both args are zero.
-	mov	a, #0
+	clrb	a
 	ret
 
 2:
@@ -151,7 +151,7 @@
 	bc	$ybig_cmpsf	; branch if X < Y
 	bnz	$xbig_cmpsf	; branch if X > Y
 
-	mov	a, #0
+	clrb	a
 	ret
 
 xbig_cmpsf:			; |X| > |Y| so return A = 1 if pos, 0xff if neg
@@ -285,7 +285,7 @@
 	movw	r10, #0x7fff
 	ret
 	;; -inf
-2:	mov	r8, #0
+2:	clrb	r8
 	mov	r10, #0x8000
 	ret
 	
@@ -302,10 +302,10 @@
 	clr1	a.7
 	call	$!__int_fixunssfsi
 
-	movw	ax, #0
+	clrw	ax
 	subw	ax, r8
 	movw	r8, ax
-	movw	ax, #0
+	clrw	ax
         sknc
         decw    ax
         subw    ax, r10
@@ -410,7 +410,7 @@
 	set1	a.7
 
 	;; Clear B:C:R12:R13
-	movw	bc, #0
+	clrw	bc
 	movw	r12, #0
 
 	;; Shift bits from the mantissa (A:X:R10) into (B:C:R12:R13),
@@ -482,10 +482,10 @@
 
 	;; If negative convert to positive ...
 	movw 	hl, ax
-	movw	ax, #0
+	clrw	ax
 	subw	ax, bc
 	movw	bc, ax
-	movw	ax, #0
+	clrw	ax
 	sknc
 	decw	ax
 	subw	ax, hl
@@ -533,7 +533,7 @@
 	bnz	$1f
 	movw	ax, bc
 	cmpw	ax, #0
-	movw	ax, #0
+	clrw	ax
 	bnz	$1f
 
 	;; Return 0.0
Index: libgcc/config/rl78/fpmath-sf.S
===================================================================
--- libgcc/config/rl78/fpmath-sf.S	(revision 3174)
+++ libgcc/config/rl78/fpmath-sf.S	(working copy)
@@ -87,7 +87,7 @@
 	or	a, #0x80
 	mov	A_FRAC_H, a
 
-	mov	a, #0
+	clrb	a
 	mov	A_FRAC_HH, a
 
 	;; rounding-bit-shift
@@ -273,7 +273,7 @@
 	;; "zero out" b
 	movw	ax, A_EXP
 	movw	B_EXP, ax
-	movw	ax, #0
+	clrw	ax
 	movw	B_FRAC_L, ax
 	movw	B_FRAC_H, ax
 	br	$5f
@@ -281,7 +281,7 @@
 	;; "zero out" a
 	movw	ax, B_EXP
 	movw	A_EXP, ax
-	movw	ax, #0
+	clrw	ax
 	movw	A_FRAC_L, ax
 	movw	A_FRAC_H, ax
 
@@ -379,7 +379,7 @@
 	bt	a.7, $.L706
 	
 	;; subtraction was positive
-	mov	a, #0
+	clrb	a
 	mov	A_SIGN, a
 	br	$.L712
 
@@ -543,7 +543,7 @@
 	or	a, A_FRAC_H
 	or	a, A_FRAC_HH
 	bnz	$1f
-	movw	ax, #0
+	clrw	ax
 	movw	A_EXP, ax
 1:	
 	mov	a, A_FRAC_H
@@ -682,7 +682,7 @@
 	movw	ax, B_FRAC_H
 	movw	[sp+10], ax
 
-	movw	ax, #0
+	clrw	ax
 	movw	[sp+4], ax
 	movw	[sp+6], ax
 	movw	[sp+12], ax
@@ -867,7 +867,7 @@
 	and	a, #0x80
 	mov	r11, a
 	movw	r8, #0
-	mov	r10, #0
+	clrb	r10
 	ret
 	
 1:	
@@ -930,7 +930,7 @@
 	movw	ax, B_FRAC_H
 	movw	[sp+10], ax
 
-	movw	ax, #0
+	clrw	ax
 	movw	[sp+0], ax
 	movw	[sp+2], ax
 	movw	[sp+12], ax
Index: libgcc/config/rl78/mulsi3.S
===================================================================
--- libgcc/config/rl78/mulsi3.S	(revision 3174)
+++ libgcc/config/rl78/mulsi3.S	(working copy)
@@ -148,7 +148,7 @@
 	movw	ax, bc
 
 .Lmul_hisi_top:
-	movw	bc, #0
+	clrw	bc
 
 .Lmul_hisi_loop:
 	shrw	ax, 1