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

[Chris Lattner]

On Oct 2, 2007, at 8:29 PM, Chris Lattner wrote:

>> 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?

Ok, nevermind, you fixed this later, thanks!

-Chris

> -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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