[llvm-commits] [llvm] r39753 - /llvm/trunk/lib/Transforms/Scalar/FastDSE.cpp

[Chris Lattner]

On Jul 11, 2007, at 1:38 PM, Owen Anderson wrote:

> Author: resistor
> Date: Wed Jul 11 15:38:34 2007
> New Revision: 39753
>
> URL: http://llvm.org/viewvc/llvm-project?rev=39753&view=rev
> Log:
> Handle eliminating stores that occur right before a free.

Don't forget that "free" deallocates the whole object, not just the  
pointer passed in.  This store should be nuked:


    int *P = ...
    P[1] = 0;
    free(P);

-Chris

> Modified:
>     llvm/trunk/lib/Transforms/Scalar/FastDSE.cpp
>
> Modified: llvm/trunk/lib/Transforms/Scalar/FastDSE.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/ 
> Scalar/FastDSE.cpp?rev=39753&r1=39752&r2=39753&view=diff
>
> ====================================================================== 
> ========
> --- llvm/trunk/lib/Transforms/Scalar/FastDSE.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/FastDSE.cpp Wed Jul 11  
> 15:38:34 2007
> @@ -74,14 +74,22 @@
>    // Do a top-down walk on the BB
>    for (BasicBlock::iterator BBI = BB.begin(), BBE = BB.end(); BBI ! 
> = BBE; ++BBI) {
>      // If we find a store...
> -    if (StoreInst* S = dyn_cast<StoreInst>(BBI)) {
> -      StoreInst*& last = lastStore[S->getPointerOperand()];
> +    if (isa<StoreInst>(BBI) || isa<FreeInst>(BBI)) {
> +      Value* pointer = 0;
> +      if (StoreInst* S = dyn_cast<StoreInst>(BBI))
> +        pointer = S->getPointerOperand();
> +      else if (FreeInst* F = dyn_cast<FreeInst>(BBI))
> +        pointer = F->getPointerOperand();
> +      assert(pointer && "Not a free or a store?");
> +
> +      StoreInst*& last = lastStore[pointer];
>
>        // ... to a pointer that has been stored to before...
>        if (last) {
>
>          // ... and no other memory dependencies are between them....
> -        if (MD.getDependency(S) == last) {
> +        if (MD.getDependency(BBI) == last) {
> +
>            // Remove it!
>            MD.removeInstruction(last);
>
> @@ -96,7 +104,10 @@
>        }
>
>        // Update our most-recent-store map
> -      last =  S;
> +      if (StoreInst* S = dyn_cast<StoreInst>(BBI))
> +        last = S;
> +      else
> +        last = 0;
>      }
>    }
>
>
>
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