[DivRemPairs] Fix non-determinism in use list order.

Summary:
Use a MapVector instead of a DenseMap for RemMap since it is iteratated
over and the order of iteration can effect the order that new
instructions are created.  This can in turn effect the use list order of
div/rem input values if multiple new instructions are created that share
any input values.

Reviewers: spatel

Subscribers: mcrosier, llvm-commits

Differential Revision: https://reviews.llvm.org/D45858

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@330792 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/DivRemPairs.cpp

@@ -13,6 +13,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Scalar/DivRemPairs.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
@@ -48,7 +50,10 @@ static bool optimizeDivRem(Function &F, const TargetTransformInfo &TTI,
 
   // Insert all divide and remainder instructions into maps keyed by their
   // operands and opcode (signed or unsigned).
-  DenseMap<DivRemMapKey, Instruction *> DivMap, RemMap;
+  DenseMap<DivRemMapKey, Instruction *> DivMap;
+  // Use a MapVector for RemMap so that instructions are moved/inserted in a
+  // deterministic order.
+  MapVector<DivRemMapKey, Instruction *> RemMap;
   for (auto &BB : F) {
     for (auto &I : BB) {
       if (I.getOpcode() == Instruction::SDiv)
@@ -67,14 +72,14 @@ static bool optimizeDivRem(Function &F, const TargetTransformInfo &TTI,
   // rare than division.
   for (auto &RemPair : RemMap) {
     // Find the matching division instruction from the division map.
-    Instruction *DivInst = DivMap[RemPair.getFirst()];
+    Instruction *DivInst = DivMap[RemPair.first];
     if (!DivInst)
       continue;
 
     // We have a matching pair of div/rem instructions. If one dominates the
     // other, hoist and/or replace one.
     NumPairs++;
-    Instruction *RemInst = RemPair.getSecond();
+    Instruction *RemInst = RemPair.second;
     bool IsSigned = DivInst->getOpcode() == Instruction::SDiv;
     bool HasDivRemOp = TTI.hasDivRemOp(DivInst->getType(), IsSigned);