Remove pruning of phi nodes in MemorySSA - it makes updating harder

Reviewers: george.burgess.iv

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D24923

llvm-svn: 282419

1 files changed, 5 insertions, 40 deletions

diff --git a/llvm/lib/Transforms/Utils/MemorySSA.cpp b/llvm/lib/Transforms/Utils/MemorySSA.cpp
index 151e60643c7..e06b60484c5 100644
--- a/llvm/lib/Transforms/Utils/MemorySSA.cpp
+++ b/llvm/lib/Transforms/Utils/MemorySSA.cpp
@@ -1348,7 +1348,7 @@ void MemorySSA::OptimizeUses::optimizeUsesInBlock(
       // branch of the dominator tree first. This will guarantee this resets on
       // the smallest set of blocks.
       if (LocInfo.LowerBoundBlock && LocInfo.LowerBoundBlock != BB &&
-          !DT->dominates(LocInfo.LowerBoundBlock, BB)){
+          !DT->dominates(LocInfo.LowerBoundBlock, BB)) {
         // Reset the lower bound of things to check.
         // TODO: Some day we should be able to reset to last kill, rather than
         // 0.
@@ -1455,12 +1455,10 @@ void MemorySSA::OptimizeUses::optimizeUses() {
 }
 
 void MemorySSA::placePHINodes(
-    const SmallPtrSetImpl<BasicBlock *> &DefiningBlocks,
-    const SmallPtrSetImpl<BasicBlock *> &LiveInBlocks) {
+    const SmallPtrSetImpl<BasicBlock *> &DefiningBlocks) {
   // Determine where our MemoryPhi's should go
   ForwardIDFCalculator IDFs(*DT);
   IDFs.setDefiningBlocks(DefiningBlocks);
-  IDFs.setLiveInBlocks(LiveInBlocks);
   SmallVector<BasicBlock *, 32> IDFBlocks;
   IDFs.calculate(IDFBlocks);
 
@@ -1511,40 +1509,7 @@ void MemorySSA::buildMemorySSA() {
     if (Accesses)
       DefUseBlocks.insert(&B);
   }
-
-  // Compute live-in.
-  // Live in is normally defined as "all the blocks on the path from each def to
-  // each of it's uses".
-  // MemoryDef's are implicit uses of previous state, so they are also uses.
-  // This means we don't really have def-only instructions.  The only
-  // MemoryDef's that are not really uses are those that are of the LiveOnEntry
-  // variable (because LiveOnEntry can reach anywhere, and every def is a
-  // must-kill of LiveOnEntry).
-  // In theory, you could precisely compute live-in by using alias-analysis to
-  // disambiguate defs and uses to see which really pair up with which.
-  // In practice, this would be really expensive and difficult. So we simply
-  // assume all defs are also uses that need to be kept live.
-  // Because of this, the end result of this live-in computation will be "the
-  // entire set of basic blocks that reach any use".
-
-  SmallPtrSet<BasicBlock *, 32> LiveInBlocks;
-  SmallVector<BasicBlock *, 64> LiveInBlockWorklist(DefUseBlocks.begin(),
-                                                    DefUseBlocks.end());
-  // Now that we have a set of blocks where a value is live-in, recursively add
-  // predecessors until we find the full region the value is live.
-  while (!LiveInBlockWorklist.empty()) {
-    BasicBlock *BB = LiveInBlockWorklist.pop_back_val();
-
-    // The block really is live in here, insert it into the set.  If already in
-    // the set, then it has already been processed.
-    if (!LiveInBlocks.insert(BB).second)
-      continue;
-
-    // Since the value is live into BB, it is either defined in a predecessor or
-    // live into it to.
-    LiveInBlockWorklist.append(pred_begin(BB), pred_end(BB));
-  }
-  placePHINodes(DefiningBlocks, LiveInBlocks);
+  placePHINodes(DefiningBlocks);
 
   // Now do regular SSA renaming on the MemoryDef/MemoryUse. Visited will get
   // filled in with all blocks.
@@ -2069,8 +2034,8 @@ bool MemorySSAPrinterLegacyPass::runOnFunction(Function &F) {
 
 char MemorySSAAnalysis::PassID;
 
-MemorySSAAnalysis::Result
-MemorySSAAnalysis::run(Function &F, FunctionAnalysisManager &AM) {
+MemorySSAAnalysis::Result MemorySSAAnalysis::run(Function &F,
+                                                 FunctionAnalysisManager &AM) {
   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
   auto &AA = AM.getResult<AAManager>(F);
   return MemorySSAAnalysis::Result(make_unique<MemorySSA>(F, &AA, &DT));