[PATCH][ARM] CLZ optimization for clzsi2 and clzdi2

[Paul Brook]

>     This patch optimizes two libraries function clzsi2 and clzdi2 for
> ARM architecture v5e and above.  This helps Thumb code more than ARM
> code actually.  For ARM, gcc already uses the CLZ instruction instead
> of call clz*i2 functions.  I've tested this patch with arm-sim for
> build with both --with-arch=v5te and without and for both ARM and
> Thumb.  The C regression test produces the same results.

Sorry about the delay responding to this.

Your patch didn't handle Thumb-2 or armv6-m.
Having separate C and asm implementations seemed like more trouble than it was 
worth. The code generated for the C implementation wasn't great either, so I 
just implemented the whole thing in assembly. This means we can use 
__builtin_clz in longlong.h, and get ffs, ctz et. al. for free.

I also took the opportunity to use a reduced size clz lookup table. This 
shaves ~300 bytes off the total text size compared to the original 
implementation. While the clz function is 3 instructions longer than it would 
be with an 8-bit lookup, I'm hoping improved cache footprint will tend to 
compensate for this.

Tested on arm-none-eabi.
Applied to svn trunk.

Paul

2008-06-12  Paul Brook  <paul@codesourcery.com>

	gcc/
	* longlong.h (__arm__): Define count_leading_zeros.
	* config/arm/lib1funcs.asm (xxh, xxl, yyh, yyl): Define.
	(clzsi2, clzdi2): New functions.
	* config/arm/bpabi-v6m.S (xxh, xxl, yyh, yyl): Remove.
	* config/arm/bpabi.S (xxh, xxl, yyh, yyl): Remove.
	* config/arm/t-strongarm-elf (LIB1ASMFUNCS): Ditto.
	* config/arm/t-vxworks (LIB1ASMFUNCS): Ditto.
	* config/arm/t-pe (LIB1ASMFUNCS): Ditto.
	* config/arm/t-arm-elf (LIB1ASMFUNCS): Ditto.
	* config/arm/t-arm-coff (LIB1ASMFUNCS): Ditto.
	* config/arm/t-linux (LIB1ASMFUNCS): Ditto.
	* config/arm/t-symbian (LIB1ASMFUNCS): Ditto.
	* config/arm/t-wince-pe (LIB1ASMFUNCS): Ditto.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: patch
Type: text/x-diff
Size: 8967 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/gcc-patches/attachments/20080612/98acff7a/attachment.bin>