Revert "Add Constant Hoisting Pass" (r200034)

[oota-llvm.git] / lib / Analysis / ScalarEvolutionNormalization.cpp

diff --git a/lib/Analysis/ScalarEvolutionNormalization.cpp b/lib/Analysis/ScalarEvolutionNormalization.cpp
index 2565ae753e98581bfa297e8e7d34c16c937944f1..33036761a0b08275673c1bab683d5b21198a0794 100644 (file)
--- a/lib/Analysis/ScalarEvolutionNormalization.cpp
+++ b/lib/Analysis/ScalarEvolutionNormalization.cpp
@@ -12,7 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/Analysis/Dominators.h"
+#include "llvm/IR/Dominators.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
 #include "llvm/Analysis/ScalarEvolutionNormalization.h"
@@ -119,11 +119,19 @@ TransformImpl(const SCEV *S, Instruction *User, Value *OperandValToReplace) {
     const SCEV *Result = SE.getAddRecExpr(Operands, L, SCEV::FlagAnyWrap);
     switch (Kind) {
     case NormalizeAutodetect:
-      if (IVUseShouldUsePostIncValue(User, OperandValToReplace, L, &DT)) {
-        const SCEV *TransformedStep =
-          TransformSubExpr(AR->getStepRecurrence(SE),
-                           User, OperandValToReplace);
-        Result = SE.getMinusSCEV(Result, TransformedStep);
+      // Normalize this SCEV by subtracting the expression for the final step.
+      // We only allow affine AddRecs to be normalized, otherwise we would not
+      // be able to correctly denormalize.
+      // e.g. {1,+,3,+,2} == {-2,+,1,+,2} + {3,+,2}
+      // Normalized form:   {-2,+,1,+,2}
+      // Denormalized form: {1,+,3,+,2}
+      //
+      // However, denormalization would use the a different step expression than
+      // normalization (see getPostIncExpr), generating the wrong final
+      // expression: {-2,+,1,+,2} + {1,+,2} => {-1,+,3,+,2}
+      if (AR->isAffine() &&
+          IVUseShouldUsePostIncValue(User, OperandValToReplace, L, &DT)) {
+        Result = SE.getMinusSCEV(Result, AR->getStepRecurrence(SE));
         Loops.insert(L);
       }
 #if 0
@@ -190,7 +198,6 @@ TransformImpl(const SCEV *S, Instruction *User, Value *OperandValToReplace) {
   }
 
   llvm_unreachable("Unexpected SCEV kind!");
-  return 0;
 }
 
 /// Manage recursive transformation across an expression DAG. Revisiting