llvm dev - Nov 2009 - [LLVMdev] DeadStoreElimination: do better without TargetData

The attached patch makes DeadStoreElimination able to remove stores in 
store-store dependencies when the operand types are equal, even if there 
is no TargetData available.

/ Hans
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Re-posting with better-looking code.

Hans Wennborg wrote:
> The attached patch makes DeadStoreElimination able to remove stores in 
> store-store dependencies when the operand types are equal, even if there 
> is no TargetData available.
> 
> / Hans
> 
> 
> ------------------------------------------------------------------------
> 
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On Nov 4, 2009, at 7:21 AM, Hans Wennborg wrote:
> Re-posting with better-looking code.
Thanks, do you have a testcase showing what this does?

-Chris
>
> Hans Wennborg wrote:
>> The attached patch makes DeadStoreElimination able to remove stores  
>> in store-store dependencies when the operand types are equal, even  
>> if there is no TargetData available.
>> / Hans
>>
------------------------------------------------------------------------
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> Index: lib/Transforms/Scalar/DeadStoreElimination.cpp
> ==================================================================> ---
lib/Transforms/Scalar/DeadStoreElimination.cpp	(revision 86023)
> +++ lib/Transforms/Scalar/DeadStoreElimination.cpp	(working copy)
> @@ -117,10 +117,12 @@
>
>     // If this is a store-store dependence, then the previous store  
> is dead so
>     // long as this store is at least as big as it.
> -    if (StoreInst *DepStore =
dyn_cast<StoreInst>(InstDep.getInst()))
> -      if (TD &&
> -         
TD->getTypeStoreSize(DepStore->getOperand(0)->getType()) <> -    
TD->getTypeStoreSize(SI->getOperand(0)->getType())) {
> +    if (StoreInst *DepStore = dyn_cast<StoreInst>(InstDep.getInst 
> ())) {
> +      const Type *DepType = DepStore->getOperand(0)->getType();
> +      const Type *SIType = SI->getOperand(0)->getType();
> +      if (DepType == SIType ||
> +          (TD &&
> +          TD->getTypeStoreSize(DepType) <= TD->getTypeStoreSize 
> (SIType))) {
>         // Delete the store and now-dead instructions that feed it.
>         DeleteDeadInstruction(DepStore);
>         NumFastStores++;
> @@ -133,6 +135,7 @@
>           --BBI;
>         continue;
>       }
> +    }
>
>     // If we're storing the same value back to a pointer that we just
>     // loaded from, then the store can be removed.
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