[llvm] r330792 - [DivRemPairs] Fix non-determinism in use list order.

[Geoff Berry via llvm-commits]

Author: gberry
Date: Tue Apr 24 19:17:56 2018
New Revision: 330792

URL: http://llvm.org/viewvc/llvm-project?rev=330792&view=rev
Log:
[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

Modified:
    llvm/trunk/lib/Transforms/Scalar/DivRemPairs.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/DivRemPairs.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/DivRemPairs.cpp?rev=330792&r1=330791&r2=330792&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/DivRemPairs.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/DivRemPairs.cpp Tue Apr 24 19:17:56 2018
@@ -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,
 
   // 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,
   // 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);