GMP 6.0 miscompiles for arm-unknown-linux-gnueabihf

[Marc Glisse]

On Fri, 4 Apr 2014, Torbjorn Granlund wrote:

> "Steve M. Robbins" <steve at sumost.ca> writes:
>
>  libtool: compile:  arm-linux-gnueabihf-gcc -std=gnu99 -DHAVE_CONFIG_H -I. -
>  I../../mpn -I.. -D__GMP_WITHIN_GMP -I../.. -DOPERATION_div_qr_1n_pi1 -
>  D_FORTIFY_SOURCE=2 -g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat
>  -Werror=format-security -O3 -c div_qr_1n_pi1.c  -fPIC -DPIC -o
>  .libs/div_qr_1n_pi1.o
>  /tmp/cchR2I5u.s: Assembler messages:
>  /tmp/cchR2I5u.s:178: Error: thumb conditional instruction should be in IT
>  block -- `movcc r4,#0'
>  /tmp/cchR2I5u.s:179: Error: thumb conditional instruction should be in IT
>  block -- `movcs r4,#-1'
>  /tmp/cchR2I5u.s:419: Error: thumb conditional instruction should be in IT
>  block -- `movcc r4,#0'
>  /tmp/cchR2I5u.s:420: Error: thumb conditional instruction should be in IT
>  block -- `movcs r4,#-1'
>  make[3]: *** [div_qr_1n_pi1.lo] Error 1
> 
> These come from inline asm in the mpn/generic/div_qr_1n_pi1.c.
>
> This is a new bug, in probably in the assembler which mistakes plain old
> ARM instructions for Thumb instructions, but possibly the compiler
> passes some silly options to misdirect the assembler.
>
> What does that cempiler make of
>
> int slt(int      a,      int b) { return a < b; }
> int ult(unsigned a, unsigned b) { return a < b; }
>
> if compiled with all your wondrous extra options, plus -S?
> I suspect there will be some conditional mov instructions in there.
>
> I get:
>
> slt:	cmp	r0, r1
> 	movge	r0, #0
> 	movlt	r0, #1
> 	bx	lr
>
> ult:	cmp	r0, r1
> 	movcs	r0, #0
> 	movcc	r0, #1
> 	bx	lr
>

File is kilometers long, but the relevant part may be:

 	cmp	r0, r1
 	ite	ge
 	movge	r0, #0
 	movlt	r0, #1
 	bx	lr


-- 
Marc Glisse