__attribute__((interrupt)) trashes MMX registers

[hjl-tools]

Bugzilla Link	26411
Version	trunk
OS	All
CC	@RKSimon

Extended Description

[hjl@gnu-6 interrupt-8]$ cat z.i

typedef short __v4hi __attribute__ ((__vector_size__ (8)));
typedef int __m64 __attribute__ ((__vector_size__ (8), __may_alias__));

extern __m64 y, x;

void
__attribute__((interrupt))
fn1 (void *frame)
{
  x = (__m64) __builtin_ia32_packsswb ((__v4hi) x, (__v4hi) y);
}

[hjl@gnu-6 interrupt-8]$ make z.s
/export/build/gnu/llvm-clang-bootstrap/stage1/build-x86_64-linux/bin/clang -O2 -Wall -march=nehalem -S -o z.s z.i
[hjl@gnu-6 interrupt-8]$ cat z.s

	.text
	.file	"z.i"
	.globl	fn1
	.p2align	4, 0x90
	.type	fn1,@function
fn1:                                    # @fn1
	.cfi_startproc
# BB#0:
	movq	x(%rip), %mm0
	packsswb	y(%rip), %mm0
	movq	%mm0, x(%rip)
	iretq
.Lfunc_end0:
	.size	fn1, .Lfunc_end0-fn1
	.cfi_endproc

	.ident	"clang version 3.9.0 (http://llvm.org/git/clang.git 1f64ddbc4c5d1036b68ec896765a7535537ded85) (http://llvm.org/git/llvm.git 43b517fe4e0a181b1cf20f36fd9eb92f7b32946c)"
	.section	".note.GNU-stack","",@progbits

[hjl@gnu-6 interrupt-8]$

Interrupt handler must preserve MMX and X87 states. It shouldn't be
allowed to use MMX nor x87 registers.

[SamB]

Hmm, I don't think you can trigger this from Clang without inline assembler anymore given the progress on #98272; now it tries to use SSE2 instead (after correcting for the removed __builtin function).