[llvm-commits] [Patch] Optimize integer ABS on X86

[Manman Ren]

Optimize generated code for integer ABS on X86:
        movl    %edi, %ecx
        sarl    $31, %ecx
        leal    (%rdi,%rcx), %eax
        xorl    %ecx, %eax
        ret
TO
        movl	%edi, %eax
	negl	%eax
	cmovll	%edi, %eax
	ret

This reduces code size and has better performance on sandy bridge.
There exists a target-independent DAG combine for integer ABS, which converts abs to sar+add+xor.
For X86, I tried to match this pattern back to neg+cmov. This is implemented in PerformXorCombine.

Thanks,
Manman

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