[PATCH] D19258: Loop vectorization with induction variable with non-constant step.

[Matthew Simpson via llvm-commits]

mssimpso added a subscriber: mssimpso.

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Comment at: ../lib/Transforms/Utils/LoopUtils.cpp:738-739
@@ +737,4 @@
+  else {
+    SetVector<Value *> *Set = SE->getSCEVValues(Step);
+    if (!Set || Set->size() != 1)
+      return false;
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delena wrote:
> hfinkel wrote:
> > I don't think this is a good way to handle this, because we'll run into all kinds of non-trivial situations where SCEV has computed an expression for the step that does not exactly correspond to a pre-existing IR value. We won't handle those cases, and it will be nearly impossible for a user to understand why.
> > 
> > Instead, convert StepValue in InductionDescriptor to a const SCEV *, and then when we need the Value* when generating IR, get one from the SCEVBuilder. It will reuse an existing Value* should one exist.
> I can't find a way to build a Value from SCEV. If the Step is "SCEVAddRecExpr", how do I get Value* from it? 
Elena,

I think Hal was suggesting you use a SCEVExpander to build a Value from a SCEV expression. SCEVExpander's are used elsewhere in the loop vectorizer.


Repository:
  rL LLVM

http://reviews.llvm.org/D19258