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[Bug target/58928] Different results from gcc when -mlzcnt is used
- From: "mikeb01 at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Fri, 17 Jan 2014 01:18:26 +0000
- Subject: [Bug target/58928] Different results from gcc when -mlzcnt is used
- Auto-submitted: auto-generated
- References: <bug-58928-4 at http dot gcc dot gnu dot org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58928
--- Comment #2 from Michael Barker <mikeb01 at gmail dot com> ---
> Hope helps
What hardware platform are you testing on? I'm running on Ivy Bridge:
Intel(R) Xeon(R) CPU E5620 @2.40GHz
Could you put the assembler that you see on the ticket:
With -mlzcnt:
0000000000400580 <lzcnt>:
400580: 55 push %rbp
400581: 48 89 e5 mov %rsp,%rbp
400584: 48 89 7d e8 mov %rdi,-0x18(%rbp)
400588: 48 8b 45 e8 mov -0x18(%rbp),%rax
40058c: 48 89 45 f8 mov %rax,-0x8(%rbp)
400590: f3 48 0f bd 45 f8 lzcnt -0x8(%rbp),%rax
400596: 48 98 cltq
400598: 5d pop %rbp
400599: c3 retq
Without -mlzcnt:
0000000000400580 <lzcnt>:
400580: 55 push %rbp
400581: 48 89 e5 mov %rsp,%rbp
400584: 48 89 7d e8 mov %rdi,-0x18(%rbp)
400588: 48 8b 45 e8 mov -0x18(%rbp),%rax
40058c: 48 89 45 f8 mov %rax,-0x8(%rbp)
400590: 48 0f bd 45 f8 bsr -0x8(%rbp),%rax
400595: 48 83 f0 3f xor $0x3f,%rax
400599: 48 98 cltq
40059b: 5d pop %rbp
40059c: c3 retq