Reapply r112432, now that the real problem is addressed.

llvm-svn: 112667

1 files changed, 9 insertions, 4 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 795232b7cec..b892d85f9f4 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3332,11 +3332,16 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
     // LLVM IR canonical form means we need only traverse the left operands.
     SmallVector<const SCEV *, 4> AddOps;
     AddOps.push_back(getSCEV(U->getOperand(1)));
-    for (Value *Op = U->getOperand(0);
-         Op->getValueID() == Instruction::Add + Value::InstructionVal;
-         Op = U->getOperand(0)) {
+    for (Value *Op = U->getOperand(0); ; Op = U->getOperand(0)) {
+      unsigned Opcode = Op->getValueID() - Value::InstructionVal;
+      if (Opcode != Instruction::Add && Opcode != Instruction::Sub)
+        break;
       U = cast<Operator>(Op);
-      AddOps.push_back(getSCEV(U->getOperand(1)));
+      const SCEV *Op1 = getSCEV(U->getOperand(1));
+      if (Opcode == Instruction::Sub)
+        AddOps.push_back(getNegativeSCEV(Op1));
+      else
+        AddOps.push_back(Op1);
     }
     AddOps.push_back(getSCEV(U->getOperand(0)));
     return getAddExpr(AddOps);