[Bug c/21535] New: Empty inline assembly cause the generated code to be wrong?

[yhlin at sdesigns dot com]

Two C file (p.c and q.c) attached bellows. With an inline assembly
line (even just a comment), the code sequence is different. As a
result, the function foo() in q.c is working OK but not the foo()
in p.c.

*** Command line ***
$ /utils/gcc/3.4.3/mipsel-linux-uclibc/i386/bin/mipsel-linux-gcc -v
Reading specs from
/utils/gcc/3.4.3/mipsel-linux-uclibc/i386/lib/gcc/mipsel-linux-uclibc/3.4.3/specs
Configured with:
/home/YH/MIPS/BR/buildroot/toolchain_build_mipsel/gcc-3.4.3/configure
--prefix=/utils/gcc/3.4.3/mipsel-linux-uclibc/i386 --build=i386-pc-linux-gnu
--host=i386-pc-linux-gnu --target=mipsel-linux-uclibc --enable-languages=c,c++
--enable-shared --disable-__cxa_atexit --enable-target-optspace --with-gnu-ld
--disable-nls --enable-multilib --enable-sjlj-exceptions
Thread model: posix
gcc version 3.4.3

$ /utils/gcc/3.4.3/mipsel-linux-uclibc/i386/bin/mipsel-linux-gcc -mno-abicalls
-O2 -c -o p.o p.c
$ /utils/gcc/3.4.3/mipsel-linux-uclibc/i386/bin/mipsel-linux-objdump -S p.o > p.dasm

$ /utils/gcc/3.4.3/mipsel-linux-uclibc/i386/bin/mipsel-linux-gcc -mno-abicalls
-O2 -c -o q.o q.c
$ /utils/gcc/3.4.3/mipsel-linux-uclibc/i386/bin/mipsel-linux-objdump -S q.o > q.dasm

==== p.c ====

int foo(int x, int y, int z)
{
__asm__ __volatile__ ("/* TEST */\n");
	return((x + y) / z);
}

==== end of p.c ====

==== q.c ====

int foo(int x, int y, int z)
{
// __asm__ __volatile__ ("/* TEST */\n");
	return((x + y) / z);
}

==== end of q.c ====

====> with the inline assembly (p.dasm)

p.o:     file format elf32-tradlittlemips

Disassembly of section .text:

00000000 <foo>:
   0:	00851021 	addu	v0,a0,a1
   4:	14c00002 	bnez	a2,10 <foo+0x10>
   8:	0046001a 	div	zero,v0,a2
   c:	0007000d 	break	0x7
  10:	00001012 	mflo	v0
  14:	03e00008 	jr	ra
  18:	00000000 	nop
  1c:	00000000 	nop

====> without the inline assembly (q.dasm)

q.o:     file format elf32-tradlittlemips

Disassembly of section .text:

00000000 <foo>:
   0:	00851021 	addu	v0,a0,a1
   4:	0046001a 	div	zero,v0,a2
   8:	14c00002 	bnez	a2,14 <foo+0x14>
   c:	00000000 	nop
  10:	0007000d 	break	0x7
  14:	00001012 	mflo	v0
  18:	03e00008 	jr	ra
  1c:	00000000 	nop

----> assembly file (p.s)

	.file	1 "p.c"
	.section .mdebug.abi32
	.previous
	.text
	.align	2
	.globl	foo
	.ent	foo
	.type	foo, @function
foo:
	.frame	$sp,0,$31		# vars= 0, regs= 0/0, args= 0, gp= 0
	.mask	0x00000000,0
	.fmask	0x00000000,0
#APP
	/* TEST */

#NO_APP
	addu	$2,$4,$5
	div	$0,$2,$6
	bne	$6,$0,1f
	break	7
1:
	mflo	$2
	j	$31
	.end	foo
	.ident	"GCC: (GNU) 3.4.3"

----> assembly file (q.s)

	.file	1 "q.c"
	.section .mdebug.abi32
	.previous
	.text
	.align	2
	.globl	foo
	.ent	foo
	.type	foo, @function
foo:
	.frame	$sp,0,$31		# vars= 0, regs= 0/0, args= 0, gp= 0
	.mask	0x00000000,0
	.fmask	0x00000000,0
	.set	noreorder
	.set	nomacro
	
	addu	$2,$4,$5
	div	$0,$2,$6
	bne	$6,$0,1f
	nop
	break	7
1:
	mflo	$2
	j	$31
	nop

	.set	macro
	.set	reorder
	.end	foo
	.ident	"GCC: (GNU) 3.4.3"

-- 
           Summary: Empty inline assembly cause the generated code to be
                    wrong?
           Product: gcc
           Version: 3.4.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: yhlin at sdesigns dot com
                CC: gcc-bugs at gcc dot gnu dot org,yhlin at sdesigns dot
                    com
 GCC build triplet: i686-pc-linux
  GCC host triplet: i686-pc-linux
GCC target triplet: mipsel-linux-gcc


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21535