[PATCH] Teaching loop simplify to preserve LCSSA

[Dinesh Dwivedi]

Added parameter to SimplifyLoop to selectively KeepSingleValuePHIs. I am looking in to making LoopSimplify pass preserve LCSSA

http://reviews.llvm.org/D2986

Files:
  include/llvm/Transforms/Utils/LoopUtils.h
  lib/Transforms/Utils/LoopSimplify.cpp
  lib/Transforms/Utils/LoopUnroll.cpp

Index: include/llvm/Transforms/Utils/LoopUtils.h
===================================================================
--- include/llvm/Transforms/Utils/LoopUtils.h
+++ include/llvm/Transforms/Utils/LoopUtils.h
@@ -32,7 +32,8 @@
 /// will optionally update \c AliasAnalysis and \c ScalarEvolution analyses if
 /// passed into it.
 bool simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, Pass *PP,
-                  AliasAnalysis *AA = nullptr, ScalarEvolution *SE = nullptr);
+                  AliasAnalysis *AA = nullptr, ScalarEvolution *SE = nullptr,
+                  bool KeepSingleValuePHIs = false);
 
 /// \brief Put loop into LCSSA form.
 ///
Index: lib/Transforms/Utils/LoopSimplify.cpp
===================================================================
--- lib/Transforms/Utils/LoopSimplify.cpp
+++ lib/Transforms/Utils/LoopSimplify.cpp
@@ -473,7 +473,8 @@
 /// explicit if they accepted the analysis directly and then updated it.
 static bool simplifyOneLoop(Loop *L, SmallVectorImpl<Loop *> &Worklist,
                             AliasAnalysis *AA, DominatorTree *DT, LoopInfo *LI,
-                            ScalarEvolution *SE, Pass *PP) {
+                            ScalarEvolution *SE, Pass *PP,
+                            bool KeepSingleValuePHIs = false) {
   bool Changed = false;
 ReprocessLoop:
 
@@ -699,17 +700,18 @@
       }
       DT->eraseNode(ExitingBlock);
 
-      BI->getSuccessor(0)->removePredecessor(ExitingBlock);
-      BI->getSuccessor(1)->removePredecessor(ExitingBlock);
+      BI->getSuccessor(0)->removePredecessor(ExitingBlock, KeepSingleValuePHIs);
+      BI->getSuccessor(1)->removePredecessor(ExitingBlock, KeepSingleValuePHIs);
       ExitingBlock->eraseFromParent();
     }
   }
 
   return Changed;
 }
 
 bool llvm::simplifyLoop(Loop *L, DominatorTree *DT, LoopInfo *LI, Pass *PP,
-                        AliasAnalysis *AA, ScalarEvolution *SE) {
+                        AliasAnalysis *AA, ScalarEvolution *SE,
+                        bool KeepSingleValuePHIs) {
   bool Changed = false;
 
   // Worklist maintains our depth-first queue of loops in this nest to process.
@@ -726,7 +728,8 @@
   }
 
   while (!Worklist.empty())
-    Changed |= simplifyOneLoop(Worklist.pop_back_val(), Worklist, AA, DT, LI, SE, PP);
+    Changed |= simplifyOneLoop(Worklist.pop_back_val(), Worklist, AA, DT, LI,
+                               SE, PP, KeepSingleValuePHIs);
 
   return Changed;
 }
Index: lib/Transforms/Utils/LoopUnroll.cpp
===================================================================
--- lib/Transforms/Utils/LoopUnroll.cpp
+++ lib/Transforms/Utils/LoopUnroll.cpp
@@ -484,9 +484,9 @@
     if (!OuterL && !CompletelyUnroll)
       OuterL = L;
     if (OuterL) {
-      ScalarEvolution *SE = PP->getAnalysisIfAvailable<ScalarEvolution>();
-      simplifyLoop(OuterL, DT, LI, PP, /*AliasAnalysis*/ nullptr, SE);
-      formLCSSARecursively(*OuterL, *DT, SE);
+      simplifyLoop(OuterL, DT, LI, PP, /*AliasAnalysis*/ 0,
+                   PP->getAnalysisIfAvailable<ScalarEvolution>(),
+                   /* KeepSingleValuePHIs = */ true);
     }
   }
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