[ScalarEvolution] refactor: extract interface getGEPExpr

Summary:
This allows other passes (such as SLSR) to compute the SCEV expression for an
imaginary GEP.

Test Plan: no regression

Reviewers: atrick, sanjoy

Reviewed By: sanjoy

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9786

llvm-svn: 237589

1 files changed, 18 insertions, 15 deletions

diff --git a/llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
index 8c147ff1f7d..453503ab61d 100644
--- a/llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
@@ -509,31 +509,34 @@ void StraightLineStrengthReduce::allocateCandidatesAndFindBasisForGEP(
   if (GEP->getType()->isVectorTy())
     return;
 
-  const SCEV *GEPExpr = SE->getSCEV(GEP);
-  Type *IntPtrTy = DL->getIntPtrType(GEP->getType());
+  SmallVector<const SCEV *, 4> IndexExprs;
+  for (auto I = GEP->idx_begin(); I != GEP->idx_end(); ++I)
+    IndexExprs.push_back(SE->getSCEV(*I));
 
   gep_type_iterator GTI = gep_type_begin(GEP);
-  for (auto I = GEP->idx_begin(); I != GEP->idx_end(); ++I) {
+  for (unsigned I = 1, E = GEP->getNumOperands(); I != E; ++I) {
     if (!isa<SequentialType>(*GTI++))
       continue;
-    Value *ArrayIdx = *I;
-    // Compute the byte offset of this index.
+
+    const SCEV *OrigIndexExpr = IndexExprs[I - 1];
+    IndexExprs[I - 1] = SE->getConstant(OrigIndexExpr->getType(), 0);
+
+    // The base of this candidate is GEP's base plus the offsets of all
+    // indices except this current one.
+    const SCEV *BaseExpr = SE->getGEPExpr(GEP->getSourceElementType(),
+                                          SE->getSCEV(GEP->getPointerOperand()),
+                                          IndexExprs, GEP->isInBounds());
+    Value *ArrayIdx = GEP->getOperand(I);
     uint64_t ElementSize = DL->getTypeAllocSize(*GTI);
-    const SCEV *ElementSizeExpr = SE->getSizeOfExpr(IntPtrTy, *GTI);
-    const SCEV *ArrayIdxExpr = SE->getSCEV(ArrayIdx);
-    ArrayIdxExpr = SE->getTruncateOrSignExtend(ArrayIdxExpr, IntPtrTy);
-    const SCEV *LocalOffset =
-        SE->getMulExpr(ArrayIdxExpr, ElementSizeExpr, SCEV::FlagNSW);
-    // The base of this candidate equals GEPExpr less the byte offset of this
-    // index.
-    const SCEV *Base = SE->getMinusSCEV(GEPExpr, LocalOffset);
-    factorArrayIndex(ArrayIdx, Base, ElementSize, GEP);
+    factorArrayIndex(ArrayIdx, BaseExpr, ElementSize, GEP);
     // When ArrayIdx is the sext of a value, we try to factor that value as
     // well.  Handling this case is important because array indices are
     // typically sign-extended to the pointer size.
     Value *TruncatedArrayIdx = nullptr;
     if (match(ArrayIdx, m_SExt(m_Value(TruncatedArrayIdx))))
-      factorArrayIndex(TruncatedArrayIdx, Base, ElementSize, GEP);
+      factorArrayIndex(TruncatedArrayIdx, BaseExpr, ElementSize, GEP);
+
+    IndexExprs[I - 1] = OrigIndexExpr;
   }
 }