[llvm-commits] [llvm] r166454 - /llvm/trunk/lib/Transforms/Utils/PromoteMemoryToRegister.cpp

[Craig Topper]

On Mon, Oct 22, 2012 at 5:23 PM, Julien Lerouge <jlerouge at apple.com> wrote:

> Author: jlerouge
> Date: Mon Oct 22 19:23:46 2012
> New Revision: 166454
>
> URL: http://llvm.org/viewvc/llvm-project?rev=166454&view=rev
> Log:
> Explain why DenseMap is still used here instead of MapVector.
>
> Modified:
>     llvm/trunk/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
>
> Modified: llvm/trunk/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/PromoteMemoryToRegister.cpp?rev=166454&r1=166453&r2=166454&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Utils/PromoteMemoryToRegister.cpp (original)
> +++ llvm/trunk/lib/Transforms/Utils/PromoteMemoryToRegister.cpp Mon Oct 22
> 19:23:46 2012
> @@ -212,7 +212,11 @@
>      ///
>      DenseMap<AllocaInst*, unsigned>  AllocaLookup;
>
> -    /// NewPhiNodes - The PhiNodes we're adding.
> +    /// NewPhiNodes - The PhiNodes we're adding.  That map is used to
> simplify
> +    /// some Phi nodes as we iterate over it, so it should have
> deterministic
> +    /// iterators.  We could use a MapVector, but since we already
> maintain a
> +    /// map from BasicBlock* to a stable numbering (BBNumbers), the
> DenseMap is
> +    /// more efficient (also supports removal).
>      ///
>      DenseMap<std::pair<unsigned, unsigned>, PHINode*> NewPhiNodes;
>
> @@ -588,6 +592,10 @@
>    while (EliminatedAPHI) {
>      EliminatedAPHI = false;
>
> +    // Iterating over NewPhiNodes is deterministic, so it is safe to try
> to
> +    // simplify and RUAW them as we go.  If it was not, we could add uses
> to
> +    // the values we replace with in a non deterministic order, thus
> creating
> +    // non deterministic def->use chains.
>

Isn't the acronym RAUW not RUAW?


>      for (DenseMap<std::pair<unsigned, unsigned>, PHINode*>::iterator I =
>             NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E;) {
>        PHINode *PN = I->second;
>
>
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-- 
~Craig
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