Make instcombine not remove Phi nodes when LCSSA is live.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@29083 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 51 insertions, 47 deletions

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index e48953b..ebefdb3 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -96,6 +96,7 @@ namespace {
 
     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
       AU.addRequired<TargetData>();
+      AU.addPreservedID(LCSSAID);
       AU.setPreservesCFG();
     }
 
@@ -6251,56 +6252,59 @@ static bool DeadPHICycle(PHINode *PN, std::set<PHINode*> &PotentiallyDeadPHIs) {
 // PHINode simplification
 //
 Instruction *InstCombiner::visitPHINode(PHINode &PN) {
-  if (Value *V = PN.hasConstantValue())
-    return ReplaceInstUsesWith(PN, V);
-
-  // If the only user of this instruction is a cast instruction, and all of the
-  // incoming values are constants, change this PHI to merge together the casted
-  // constants.
-  if (PN.hasOneUse())
-    if (CastInst *CI = dyn_cast<CastInst>(PN.use_back()))
-      if (CI->getType() != PN.getType()) {  // noop casts will be folded
-        bool AllConstant = true;
-        for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
-          if (!isa<Constant>(PN.getIncomingValue(i))) {
-            AllConstant = false;
-            break;
-          }
-        if (AllConstant) {
-          // Make a new PHI with all casted values.
-          PHINode *New = new PHINode(CI->getType(), PN.getName(), &PN);
-          for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
-            Constant *OldArg = cast<Constant>(PN.getIncomingValue(i));
-            New->addIncoming(ConstantExpr::getCast(OldArg, New->getType()),
-                             PN.getIncomingBlock(i));
-          }
+  // If LCSSA is around, don't nuke PHIs.
+  if (!mustPreserveAnalysisID(LCSSAID)) {
+    if (Value *V = PN.hasConstantValue())
+      return ReplaceInstUsesWith(PN, V);
+
+    // If the only user of this instruction is a cast instruction, and all of
+    //the incoming values are constants, change this PHI to merge together the 
+    // casted constants.
+    if (PN.hasOneUse())
+      if (CastInst *CI = dyn_cast<CastInst>(PN.use_back()))
+        if (CI->getType() != PN.getType()) {  // noop casts will be folded
+          bool AllConstant = true;
+          for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
+            if (!isa<Constant>(PN.getIncomingValue(i))) {
+              AllConstant = false;
+              break;
+            }
+          if (AllConstant) {
+            // Make a new PHI with all casted values.
+            PHINode *New = new PHINode(CI->getType(), PN.getName(), &PN);
+            for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
+              Constant *OldArg = cast<Constant>(PN.getIncomingValue(i));
+              New->addIncoming(ConstantExpr::getCast(OldArg, New->getType()),
+                               PN.getIncomingBlock(i));
+            }
 
-          // Update the cast instruction.
-          CI->setOperand(0, New);
-          WorkList.push_back(CI);    // revisit the cast instruction to fold.
-          WorkList.push_back(New);   // Make sure to revisit the new Phi
-          return &PN;                // PN is now dead!
+            // Update the cast instruction.
+            CI->setOperand(0, New);
+            WorkList.push_back(CI);    // revisit the cast instruction to fold.
+            WorkList.push_back(New);   // Make sure to revisit the new Phi
+            return &PN;                // PN is now dead!
+          }
         }
-      }
-
-  // If all PHI operands are the same operation, pull them through the PHI,
-  // reducing code size.
-  if (isa<Instruction>(PN.getIncomingValue(0)) &&
-      PN.getIncomingValue(0)->hasOneUse())
-    if (Instruction *Result = FoldPHIArgOpIntoPHI(PN))
-      return Result;
-
-  // If this is a trivial cycle in the PHI node graph, remove it.  Basically, if
-  // this PHI only has a single use (a PHI), and if that PHI only has one use (a
-  // PHI)... break the cycle.
-  if (PN.hasOneUse())
-    if (PHINode *PU = dyn_cast<PHINode>(PN.use_back())) {
-      std::set<PHINode*> PotentiallyDeadPHIs;
-      PotentiallyDeadPHIs.insert(&PN);
-      if (DeadPHICycle(PU, PotentiallyDeadPHIs))
-        return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
-    }
 
+    // If all PHI operands are the same operation, pull them through the PHI,
+    // reducing code size.
+    if (isa<Instruction>(PN.getIncomingValue(0)) &&
+        PN.getIncomingValue(0)->hasOneUse())
+      if (Instruction *Result = FoldPHIArgOpIntoPHI(PN))
+        return Result;
+
+    // If this is a trivial cycle in the PHI node graph, remove it.  Basically,
+    // if this PHI only has a single use (a PHI), and if that PHI only has one 
+    // use (a PHI)... break the cycle.
+    if (PN.hasOneUse())
+      if (PHINode *PU = dyn_cast<PHINode>(PN.use_back())) {
+        std::set<PHINode*> PotentiallyDeadPHIs;
+        PotentiallyDeadPHIs.insert(&PN);
+        if (DeadPHICycle(PU, PotentiallyDeadPHIs))
+          return ReplaceInstUsesWith(PN, UndefValue::get(PN.getType()));
+      }
+  }
+  
   return 0;
 }