Change PHINode::hasConstantValue to have a DominatorTree argument

instead of a bool argument, and to do the dominator check itself.
This makes it eaiser to use when DominatorTree information is
available.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80920 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Instructions.h

@@ -31,6 +31,7 @@ class ConstantInt;
 class ConstantRange;
 class APInt;
 class LLVMContext;
+class DominatorTree;
 
 //===----------------------------------------------------------------------===//
 //                             AllocationInst Class
@@ -1950,7 +1951,12 @@ public:
   /// hasConstantValue - If the specified PHI node always merges together the
   /// same value, return the value, otherwise return null.
   ///
-  Value *hasConstantValue(bool AllowNonDominatingInstruction = false) const;
+  /// If the PHI has undef operands, but all the rest of the operands are
+  /// some unique value, return that value if it can be proved that the
+  /// value dominates the PHI. If DT is null, use a conservative check,
+  /// otherwise use DT to test for dominance.
+  ///
+  Value *hasConstantValue(DominatorTree *DT = 0) const;
 
   /// Methods for support type inquiry through isa, cast, and dyn_cast:
   static inline bool classof(const PHINode *) { return true; }

lib/Transforms/Scalar/GVN.cpp

@@ -769,7 +769,7 @@ static bool isSafeReplacement(PHINode* p, Instruction* inst) {
 }
 
 Value* GVN::CollapsePhi(PHINode* p) {
-  Value* constVal = p->hasConstantValue();
+  Value* constVal = p->hasConstantValue(DT);
   if (!constVal) return 0;
   
   Instruction* inst = dyn_cast<Instruction>(constVal);

lib/Transforms/Utils/BasicBlockUtils.cpp

@@ -429,15 +429,12 @@ BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
     PN->addIncoming(InVal, NewBB);
     
     // Check to see if we can eliminate this phi node.
-    if (Value *V = PN->hasConstantValue(DT != 0)) {
+    if (Value *V = PN->hasConstantValue(DT)) {
-      Instruction *I = dyn_cast<Instruction>(V);
-      if (!I || DT == 0 || DT->dominates(I, PN)) {
       PN->replaceAllUsesWith(V);
       if (AA) AA->deleteValue(PN);
       PN->eraseFromParent();
     }
   }
-  }
   
   return NewBB;
 }

lib/Transforms/Utils/LoopSimplify.cpp

@@ -255,7 +255,7 @@ ReprocessLoop:
   PHINode *PN;
   for (BasicBlock::iterator I = L->getHeader()->begin();
        (PN = dyn_cast<PHINode>(I++)); )
-    if (Value *V = PN->hasConstantValue()) {
+    if (Value *V = PN->hasConstantValue(DT)) {
       if (AA) AA->deleteValue(PN);
       PN->replaceAllUsesWith(V);
       PN->eraseFromParent();
@@ -417,8 +417,7 @@ static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT,
   for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
     PHINode *PN = cast<PHINode>(I);
     ++I;
-    if (Value *V = PN->hasConstantValue())
+    if (Value *V = PN->hasConstantValue(DT)) {
-      if (!isa<Instruction>(V) || DT->dominates(cast<Instruction>(V), PN)) {
       // This is a degenerate PHI already, don't modify it!
       PN->replaceAllUsesWith(V);
       if (AA) AA->deleteValue(PN);

lib/Transforms/Utils/PromoteMemoryToRegister.cpp

@@ -494,9 +494,7 @@ void PromoteMem2Reg::run() {
       PHINode *PN = I->second;
       
       // If this PHI node merges one value and/or undefs, get the value.
-      if (Value *V = PN->hasConstantValue(true)) {
+      if (Value *V = PN->hasConstantValue(&DT)) {
-        if (!isa<Instruction>(V) ||
-            properlyDominates(cast<Instruction>(V), PN)) {
         if (AST && isa<PointerType>(PN->getType()))
           AST->deleteValue(PN);
         PN->replaceAllUsesWith(V);
@@ -505,7 +503,6 @@ void PromoteMem2Reg::run() {
         EliminatedAPHI = true;
         continue;
       }
-      }
       ++I;
     }
   }

lib/VMCore/Instructions.cpp

@@ -17,6 +17,7 @@
 #include "llvm/Function.h"
 #include "llvm/Instructions.h"
 #include "llvm/Operator.h"
+#include "llvm/Analysis/Dominators.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/CallSite.h"
 #include "llvm/Support/ConstantRange.h"
@@ -226,7 +227,12 @@ void PHINode::resizeOperands(unsigned NumOps) {
 /// hasConstantValue - If the specified PHI node always merges together the same
 /// value, return the value, otherwise return null.
 ///
-Value *PHINode::hasConstantValue(bool AllowNonDominatingInstruction) const {
+/// If the PHI has undef operands, but all the rest of the operands are
+/// some unique value, return that value if it can be proved that the
+/// value dominates the PHI. If DT is null, use a conservative check,
+/// otherwise use DT to test for dominance.
+///
+Value *PHINode::hasConstantValue(DominatorTree *DT) const {
   // If the PHI node only has one incoming value, eliminate the PHI node...
   if (getNumIncomingValues() == 1) {
     if (getIncomingValue(0) != this)   // not  X = phi X
@@ -260,12 +266,19 @@ Value *PHINode::hasConstantValue(bool AllowNonDominatingInstruction) const {
   // instruction, we cannot always return X as the result of the PHI node.  Only
   // do this if X is not an instruction (thus it must dominate the PHI block),
   // or if the client is prepared to deal with this possibility.
-  if (HasUndefInput && !AllowNonDominatingInstruction)
+  if (HasUndefInput)
-    if (Instruction *IV = dyn_cast<Instruction>(InVal))
+    if (Instruction *IV = dyn_cast<Instruction>(InVal)) {
+      if (DT) {
+        // We have a DominatorTree. Do a precise test.
+        if (!DT->dominates(IV, this))
+          return 0;
+      } else {
         // If it's in the entry block, it dominates everything.
         if (IV->getParent() != &IV->getParent()->getParent()->getEntryBlock() ||
             isa<InvokeInst>(IV))
           return 0;   // Cannot guarantee that InVal dominates this PHINode.
+      }
+    }
 
   // All of the incoming values are the same, return the value now.
   return InVal;

test/Transforms/GVN/2008-07-02-Unreachable.ll

@@ -1,4 +1,4 @@
-; RUN: llvm-as < %s | opt -gvn | llvm-dis | grep undef
+; RUN: llvm-as < %s | opt -gvn | llvm-dis | grep {ret i8 \[%\]tmp3}
 ; PR2503
 
 @g_3 = external global i8		; <i8*> [#uses=2]