[LLVMdev] [PATCH] Minor fix to StackColoring to avoid needlessly clearing mem operands.

[Duncan Sands]

Hi Akira, did anything happen with this patch?

Ciao, Duncan.

On 09/05/13 04:04, Akira Hatanaka wrote:
> The following code snippet taken from StackColoring::remapInstructions clears a
> mem operand if it can't guarantee whether the memoperand's underlying value
> aliases with the merged allocas:
>
> // Update the MachineMemOperand to use the new alloca.
>   522       for (MachineInstr::mmo_iterator MM = I->memoperands_begin(),
> ....
>           // Climb up and find the original alloca.
>   532         V = GetUnderlyingObject(V);
>   533         // If we did not find one, or if the one that we found is not in our
>   534         // map, then move on.
>   535         if (!V || !isa<AllocaInst>(V)) {
>   536           // Clear mem operand since we don't know for sure that it doesn't
>   537           // alias a merged alloca.
>   538           MMO->setValue(0);
>   539           continue;
>   540         }
>
> The attached patch makes the code above less conservative. It avoids clearing a
> mem operand if its underlying value is a PseudoSourceValue and
> PseudoSourceValue::isConstant returns true. This enables MachineLICM to hoist
> loads from GOT out of a loop (see test case in stackcoloring-test.patch).
>
> Please review.
>
> Question: Why does it need to clear a mem operand if the underlying object is
> not an AllocaInst? I am not sure if I understand the reason for this.
>
>
>
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