[SCEV][LAA] Add no wrap SCEV predicates and use use them to improve strided pointer detection

Summary:
This change adds no wrap SCEV predicates with:
  - support for runtime checking
  - support for expression rewriting:
      (sext ({x,+,y}) -> {sext(x),+,sext(y)}
      (zext ({x,+,y}) -> {zext(x),+,sext(y)}

Note that we are sign extending the increment of the SCEV, even for
the zext case. This is needed to cover the fairly common case where y would
be a (small) negative integer. In order to do this, this change adds two new
flags: nusw and nssw that are applicable to AddRecExprs and permit the
transformations above.

We also change isStridedPtr in LAA to be able to make use of
these predicates. With this feature we should now always be able to
work around overflow issues in the dependence analysis.

Reviewers: mzolotukhin, sanjoy, anemet

Subscribers: mzolotukhin, sanjoy, llvm-commits, rengolin, jmolloy, hfinkel

Differential Revision: http://reviews.llvm.org/D15412

llvm-svn: 260085

1 files changed, 4 insertions, 6 deletions

diff --git a/llvm/test/Transforms/LoopVectorize/same-base-access.ll b/llvm/test/Transforms/LoopVectorize/same-base-access.ll
index 31cff0ee653..53fad8afdad 100644
--- a/llvm/test/Transforms/LoopVectorize/same-base-access.ll
+++ b/llvm/test/Transforms/LoopVectorize/same-base-access.ll
@@ -62,11 +62,9 @@ define i32 @kernel11(double* %x, double* %y, i32 %n) nounwind uwtable ssp {
 }
 
 
-
-; We don't vectorize this function because A[i*7] is scalarized, and the
-; different scalars can in theory wrap around and overwrite other scalar
-; elements. At the moment we only allow read/write access to arrays
-; that are consecutive.
+; A[i*7] is scalarized, and the different scalars can in theory wrap
+; around and overwrite other scalar elements. However we can still
+; vectorize because we can version the loop to avoid this case.
 ; 
 ; void foo(int *a) {
 ;   for (int i=0; i<256; ++i) {
@@ -78,7 +76,7 @@ define i32 @kernel11(double* %x, double* %y, i32 %n) nounwind uwtable ssp {
 ; }
 
 ; CHECK-LABEL: @func2(
-; CHECK-NOT: <4 x i32>
+; CHECK: <4 x i32>
 ; CHECK: ret
 define i32 @func2(i32* nocapture %a) nounwind uwtable ssp {
   br label %1