[PATCH] D45858: [DivRemPairs] Fix non-determinism in use list order.

[Geoff Berry via Phabricator via llvm-commits]

gberry created this revision.
gberry added a reviewer: spatel.
Herald added a subscriber: mcrosier.

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.


Repository:
  rL LLVM

https://reviews.llvm.org/D45858

Files:
  lib/Transforms/Scalar/DivRemPairs.cpp


Index: lib/Transforms/Scalar/DivRemPairs.cpp
===================================================================
--- lib/Transforms/Scalar/DivRemPairs.cpp
+++ 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 @@
 
   // 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 @@
   // 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);
 


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