[llvm-commits] [llvm] r120932 - in /llvm/trunk: lib/Target/X86/X86ISelLowering.cpp test/CodeGen/X86/select.ll

[Chris Lattner]

On Dec 5, 2010, at 2:22 PM, Evan Cheng wrote:

>> 
>> __Z4funcl:                              ## @_Z4funcl
>> 	movl	$4, %ecx                ## encoding: [0xb9,0x04,0x00,0x00,0x00]
>> 	movq	%rdi, %rax              ## encoding: [0x48,0x89,0xf8]
>> 	mulq	%rcx                    ## encoding: [0x48,0xf7,0xe1]
>> 	cmpq	$1, %rdx                ## encoding: [0x48,0x83,0xfa,0x01]
>> 	sbbq	%rdi, %rdi              ## encoding: [0x48,0x19,0xff]
>> 	notq	%rdi                    ## encoding: [0x48,0xf7,0xd7]
>> 	orq	%rax, %rdi              ## encoding: [0x48,0x09,0xc7]
>> 	jmp	__Znam                  ## TAILCALL
>>                                       ## encoding: [0xeb,A]
> 
> Why is this an improvement?

cmov is high latency and generally bad, but this also helps if the other value is an imm or load, because those can be folded into orq but not into cmov.

-Chris