[PR16756] Use SSAUpdaterBulk in JumpThreading.

Summary:
SSAUpdater is a bottleneck in JumpThreading, and this patch improves the
situation by using SSAUpdaterBulk instead.

Compile time impact: no noticable changes on CTMark, a big improvement
on the test from PR16756.

Reviewers: dberlin, davide, MatzeB

Subscribers: llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D44282

llvm-svn: 329644

diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 29c7077..2caf6b7 100644 (file)
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -66,6 +66,7 @@
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Cloning.h"
 #include "llvm/Transforms/Utils/SSAUpdater.h"
+#include "llvm/Transforms/Utils/SSAUpdaterBulk.h"
 #include "llvm/Transforms/Utils/ValueMapper.h"
 #include <algorithm>
 #include <cassert>
@@ -1989,9 +1990,13 @@ bool JumpThreadingPass::ThreadEdge(BasicBlock *BB,
   // now have to update all uses of the value to use either the original value,
   // the cloned value, or some PHI derived value.  This can require arbitrary
   // PHI insertion, of which we are prepared to do, clean these up now.
-  SSAUpdater SSAUpdate;
+  SSAUpdaterBulk SSAUpdate;
   SmallVector<Use*, 16> UsesToRename;
+
+  unsigned VarNum = 0;
   for (Instruction &I : *BB) {
+    UsesToRename.clear();
+
     // Scan all uses of this instruction to see if it is used outside of its
     // block, and if so, record them in UsesToRename.
     for (Use &U : I.uses()) {
@@ -2008,19 +2013,15 @@ bool JumpThreadingPass::ThreadEdge(BasicBlock *BB,
     // If there are no uses outside the block, we're done with this instruction.
     if (UsesToRename.empty())
       continue;
+    SSAUpdate.AddVariable(VarNum, I.getName(), I.getType());
 
-    DEBUG(dbgs() << "JT: Renaming non-local uses of: " << I << "\n");
-
-    // We found a use of I outside of BB.  Rename all uses of I that are outside
-    // its block to be uses of the appropriate PHI node etc.  See ValuesInBlocks
-    // with the two values we know.
-    SSAUpdate.Initialize(I.getType(), I.getName());
-    SSAUpdate.AddAvailableValue(BB, &I);
-    SSAUpdate.AddAvailableValue(NewBB, ValueMapping[&I]);
-
-    while (!UsesToRename.empty())
-      SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
-    DEBUG(dbgs() << "\n");
+    // We found a use of I outside of BB - we need to rename all uses of I that
+    // are outside its block to be uses of the appropriate PHI node etc.
+    SSAUpdate.AddAvailableValue(VarNum, BB, &I);
+    SSAUpdate.AddAvailableValue(VarNum, NewBB, ValueMapping[&I]);
+    for (auto U : UsesToRename)
+      SSAUpdate.AddUse(VarNum, U);
+    VarNum++;
   }
 
   // Ok, NewBB is good to go.  Update the terminator of PredBB to jump to
@@ -2037,6 +2038,10 @@ bool JumpThreadingPass::ThreadEdge(BasicBlock *BB,
                      {DominatorTree::Insert, PredBB, NewBB},
                      {DominatorTree::Delete, PredBB, BB}});
 
+  // Apply all updates we queued with DDT and get the updated Dominator Tree.
+  DominatorTree *DT = &DDT->flush();
+  SSAUpdate.RewriteAllUses(DT);
+
   // At this point, the IR is fully up to date and consistent.  Do a quick scan
   // over the new instructions and zap any that are constants or dead.  This
   // frequently happens because of phi translation.