[llvm-commits] [llvm] r42546 - /llvm/trunk/lib/Target/X86/README.txt

[Chris Lattner]

> URL: http://llvm.org/viewvc/llvm-project?rev=42546&view=rev
> Log:
> Another missed optimization.

Hi Bill,

Thank you for tracking these down.  However, without .ll files or .c  
files to reproduce this, they are somewhat useless.  In the example  
below, if I wanted to work on this, how would I demonstrate the issue?

-Chris

> Modified:
>     llvm/trunk/lib/Target/X86/README.txt
>
> Modified: llvm/trunk/lib/Target/X86/README.txt
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/ 
> README.txt?rev=42546&r1=42545&r2=42546&view=diff
>
> ====================================================================== 
> ========
> --- llvm/trunk/lib/Target/X86/README.txt (original)
> +++ llvm/trunk/lib/Target/X86/README.txt Tue Oct  2 15:42:59 2007
> @@ -1239,3 +1239,31 @@
>
>  // 
> ===------------------------------------------------------------------- 
> --===//
>
> +The following code:
> +
> +LBB3_5:	# bb114.preheader
> +	movswl	-68(%ebp), %eax
> +	movl	$32, %ecx
> +	movl	%ecx, -80(%ebp)
> +	subl	%eax, -80(%ebp)
> +	movswl	-52(%ebp), %eax
> +	movl	%ecx, -84(%ebp)
> +	subl	%eax, -84(%ebp)
> +	movswl	-70(%ebp), %eax
> +	movl	%ecx, -88(%ebp)
> +	subl	%eax, -88(%ebp)
> +	movswl	-50(%ebp), %eax
> +	subl	%eax, %ecx
> +	movl	%ecx, -76(%ebp)
> +	movswl	-42(%ebp), %eax
> +	movl	%eax, -92(%ebp)
> +	movswl	-66(%ebp), %eax
> +	movl	%eax, -96(%ebp)
> +	movw	$0, -98(%ebp)
> +
> +has redundant subtractions of %eax from a stack slot. However, % 
> ecx doesn't
> +change, so we could simply subtract %eax from %ecx first and then  
> use %ecx (or
> +vice-versa).
> +
> +// 
> ===------------------------------------------------------------------- 
> --===//
> +
>
>
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