[PATCH] [LoopVectorize] Induction variables: support arbitrary constant step
hfinkel at anl.gov
hfinkel at anl.gov
Tue Jan 27 08:10:09 PST 2015
================
Comment at: lib/Transforms/Vectorize/LoopVectorize.cpp:722
@@ +721,3 @@
+ /// For pointer induction, returns StartValue[Index * StepValue].
+ Value *transform(IRBuilder<> &B, Value *Index) const {
+ switch (IK) {
----------------
aschwaighofer wrote:
> hfinkel wrote:
> > Given that we don't vectorize loops with wrap-around index spaces, as far as I know, we should be able to add nsw (or nuw or both) flags on these operations. Please do so when possible.
> Hal, I don't think this is safe. Consider the following example. The canonical induction variable does not wrap but the derived one does.
>
> int test(int *a) {
> int r = 0;
> uint64_t idx2=0;
> for (uint64_t i = 0 ; i < UINT64_MAX; ++i) {
> r+=a[idx2];
> idx2 += 2;
> }
> return r;
> }
Agreed. But shouldn't we be able to get the nsw/nuw flags from the original scalar operation?
(If so, but this departs too far from the scope of this patch, I'm fine with adding a FIXME and leaving this for follow-up)
http://reviews.llvm.org/D7193
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