[AVX] encoding issue with roundss instruction?

[llvmbot]

Bugzilla Link	10840
Resolution	FIXED
Resolved on	Sep 26, 2011 00:32
Version	unspecified
OS	All
Blocks	llvm/llvm-bugzilla-archive#10988
Attachments	test case
Reporter	LLVM Bugzilla Contributor
CC	@d0k,@topperc

Extended Description

If I run llvm-objdump -disassemble on the object file generated by running the attached test case through llc -filetype=obj, I get errors about invalid instruction encoding.

Specifically, if I run "llc -mattr=+avx bug.ll -o -", there is this instruction sequence toward the end:

vmulss	LCPI0_1(%rip), %xmm1, %xmm2
vroundss	$9, %xmm2, %xmm2, %xmm2
vcvttss2si	%xmm2, %edx
andl	$3, %edx

However, if I run "llc -mattr=+avx -filetype=obj bug.ll -o - | llvm-objdump - -disassemble", then the output for the corresponding part is:

 160:	c5 f2 59 15 bc 00 00 00                      	vmulss	188(%rip), %xmm1, %xmm2

llvm-objdump: warning: invalid instruction encoding
16c: d2 09 rorb %cl, (%rcx)
16e: c5 fa 2c d2 vcvttss2si %xmm2, %edx
172: 83 e2 03 andl $3, %edx

So either the wrong encoding is being generated when making object files, or llvm-objdump doesn't know about this instruction. (I hope it's the former, since I'm seeing crashes when running the generated code. :-) ).

[llvmbot]

For what it's worth, Agner Fogg's disassembler reports that that vroundss is encoded as expected, so that suggests this is a bug in llvm-objdump, not in the output from the AVX backend.

(I'll spend some time today spinning up on the AVX encodings to confirm this from the ISA spec as well.)

[bcardosolopes]

This is an assembler bug, CCing more people that may be willing to solve that!

[topperc]

This seems to be working now.

[bcardosolopes]

mentioned in issue llvm/llvm-bugzilla-archive#10988