[PATCH] [LoopVectorize] Induction variables: support arbitrary constant step

[Hao Liu]

Hi,

According to the comments, a new patch has been attached.
Review, please.

Thanks,
-Hao


================
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) {
----------------
hfinkel wrote:
> 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)
> 
Agree with you two. Several FIXMEs have been added.

================
Comment at: test/Transforms/LoopVectorize/arbitrary-induction-step.ll:7
@@ +6,3 @@
+
+; CHECK: LV: Checking a loop in "ind_plus2"
+; CHECK: LV: Did not find one integer induction var.
----------------
hfinkel wrote:
> If you're checking debug output, you'll need to add:
> 
>   ; REQUIRES: asserts
> 
> to the entire test. Please break this out into a separate test file, if you'd like to do this, to limit the reduction in test coverage for non-asserts builds.
Hal, thanks for let me know about this.
As I think it's not worth to add another file just for testing the debug info, I remove such 'CHECK' and '-debug-only'.

http://reviews.llvm.org/D7193

EMAIL PREFERENCES
  http://reviews.llvm.org/settings/panel/emailpreferences/