[LAA] Improve non-wrapping pointer detection by handling loop-invariant case.

This fixes PR26314. This patch adds new helper “isNoWrap” with detection of
loop-invariant pointer case.

Patch by Roman Shirokiy.

Ref: https://llvm.org/bugs/show_bug.cgi?id=26314

Differential Revision: http://reviews.llvm.org/D17268

llvm-svn: 272014

1 files changed, 14 insertions, 4 deletions

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index a0df64b4d0a..ff5bc595da5 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -467,7 +467,7 @@ public:
   /// (i.e. the pointers have computable bounds).
   bool canCheckPtrAtRT(RuntimePointerChecking &RtCheck, ScalarEvolution *SE,
                        Loop *TheLoop, const ValueToValueMap &Strides,
-                       bool ShouldCheckStride = false);
+                       bool ShouldCheckWrap = false);
 
   /// \brief Goes over all memory accesses, checks whether a RT check is needed
   /// and builds sets of dependent accesses.
@@ -551,10 +551,21 @@ static bool hasComputableBounds(PredicatedScalarEvolution &PSE,
   return AR->isAffine();
 }
 
+/// \brief Check whether a pointer address cannot wrap.
+static bool isNoWrap(PredicatedScalarEvolution &PSE,
+                     const ValueToValueMap &Strides, Value *Ptr, Loop *L) {
+  const SCEV *PtrScev = PSE.getSCEV(Ptr);
+  if (PSE.getSE()->isLoopInvariant(PtrScev, L))
+    return true;
+
+  int Stride = getPtrStride(PSE, Ptr, L, Strides);
+  return Stride == 1;
+}
+
 bool AccessAnalysis::canCheckPtrAtRT(RuntimePointerChecking &RtCheck,
                                      ScalarEvolution *SE, Loop *TheLoop,
                                      const ValueToValueMap &StridesMap,
-                                     bool ShouldCheckStride) {
+                                     bool ShouldCheckWrap) {
   // Find pointers with computable bounds. We are going to use this information
   // to place a runtime bound check.
   bool CanDoRT = true;
@@ -589,8 +600,7 @@ bool AccessAnalysis::canCheckPtrAtRT(RuntimePointerChecking &RtCheck,
       if (hasComputableBounds(PSE, StridesMap, Ptr, TheLoop) &&
           // When we run after a failing dependency check we have to make sure
           // we don't have wrapping pointers.
-          (!ShouldCheckStride ||
-           getPtrStride(PSE, Ptr, TheLoop, StridesMap) == 1)) {
+          (!ShouldCheckWrap || isNoWrap(PSE, StridesMap, Ptr, TheLoop))) {
         // The id of the dependence set.
         unsigned DepId;