Fix PR13851: Preserve metadata for the unswitched branch

[oota-llvm.git] / lib / Transforms / Scalar / StraightLineStrengthReduce.cpp

diff --git a/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp b/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
index 8c147ff1f7da37afdaccdf753e380da380b9da3e..f32769c241101ab41eab5a77b02ef96cf9c34d15 100644 (file)
--- a/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/StraightLineStrengthReduce.cpp
@@ -265,8 +265,10 @@ static bool isGEPFoldable(GetElementPtrInst *GEP,
       BaseOffset += DL->getStructLayout(STy)->getElementOffset(Field);
     }
   }
+
+  unsigned AddrSpace = GEP->getPointerAddressSpace();
   return TTI->isLegalAddressingMode(GEP->getType()->getElementType(), BaseGV,
-                                    BaseOffset, HasBaseReg, Scale);
+                                    BaseOffset, HasBaseReg, Scale, AddrSpace);
 }
 
 // Returns whether (Base + Index * Stride) can be folded to an addressing mode.
@@ -509,31 +511,34 @@ 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;
   }
 }
 
@@ -627,6 +632,15 @@ void StraightLineStrengthReduce::rewriteCandidateWithBasis(
       // trivially dead.
       RecursivelyDeleteTriviallyDeadInstructions(Bump);
     } else {
+      // It's tempting to preserve nsw on Bump and/or Reduced. However, it's
+      // usually unsound, e.g.,
+      //
+      // X = (-2 +nsw 1) *nsw INT_MAX
+      // Y = (-2 +nsw 3) *nsw INT_MAX
+      //   =>
+      // Y = X + 2 * INT_MAX
+      //
+      // Neither + and * in the resultant expression are nsw.
       Reduced = Builder.CreateAdd(Basis.Ins, Bump);
     }
     break;