From 616613d7a4ddc7cefce53b2bfe3fdcdec6b032c2 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Fri, 27 Nov 2009 08:25:10 +0000
Subject: teach GVN's load PRE to insert computations of the address in
 predecessors where it is not available.  It's unclear how to get this
 inserted computation into GVN's scalar availability sets, Owen, help? :)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89997 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/MemoryDependenceAnalysis.cpp | 72 ++++++++++++++++++++++++++++---
 1 file changed, 67 insertions(+), 5 deletions(-)

(limited to 'lib/Analysis/MemoryDependenceAnalysis.cpp')

diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index bb5b76cef9..95e9437339 100644
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -752,19 +752,35 @@ PHITranslatePointer(Value *InVal, BasicBlock *CurBB, BasicBlock *Pred,
   // Handle getelementptr with at least one PHI operand.
   if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
     SmallVector<Value*, 8> GEPOps;
-    Value *APHIOp = 0;
     BasicBlock *CurBB = GEP->getParent();
     for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
-      GEPOps.push_back(GEP->getOperand(i)->DoPHITranslation(CurBB, Pred));
-      if (!isa<Constant>(GEPOps.back()))
-        APHIOp = GEPOps.back();
+      Value *GEPOp = GEP->getOperand(i);
+      // No PHI translation is needed of operands whose values are live in to
+      // the predecessor block.
+      if (!isa<Instruction>(GEPOp) ||
+          cast<Instruction>(GEPOp)->getParent() != CurBB) {
+        GEPOps.push_back(GEPOp);
+        continue;
+      }
+      
+      // If the operand is a phi node, do phi translation.
+      if (PHINode *PN = dyn_cast<PHINode>(GEPOp)) {
+        GEPOps.push_back(PN->getIncomingValueForBlock(Pred));
+        continue;
+      }
+      
+      // Otherwise, we can't PHI translate this random value defined in this
+      // block.
+      return 0;
     }
     
     // Simplify the GEP to handle 'gep x, 0' -> x etc.
     if (Value *V = SimplifyGEPInst(&GEPOps[0], GEPOps.size(), TD))
       return V;
-    
+
+
     // Scan to see if we have this GEP available.
+    Value *APHIOp = GEPOps[0];
     for (Value::use_iterator UI = APHIOp->use_begin(), E = APHIOp->use_end();
          UI != E; ++UI) {
       if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI))
@@ -787,6 +803,52 @@ PHITranslatePointer(Value *InVal, BasicBlock *CurBB, BasicBlock *Pred,
   return 0;
 }
 
+/// InsertPHITranslatedPointer - Insert a computation of the PHI translated
+/// version of 'V' for the edge PredBB->CurBB into the end of the PredBB
+/// block.
+///
+/// This is only called when PHITranslatePointer returns a value that doesn't
+/// dominate the block, so we don't need to handle the trivial cases here.
+Value *MemoryDependenceAnalysis::
+InsertPHITranslatedPointer(Value *InVal, BasicBlock *CurBB,
+                           BasicBlock *PredBB, const TargetData *TD) const {
+  // If the input value isn't an instruction in CurBB, it doesn't need phi
+  // translation.
+  Instruction *Inst = cast<Instruction>(InVal);
+  assert(Inst->getParent() == CurBB && "Doesn't need phi trans");
+
+  // Handle bitcast of PHI.
+  if (BitCastInst *BC = dyn_cast<BitCastInst>(Inst)) {
+    PHINode *BCPN = cast<PHINode>(BC->getOperand(0));
+    Value *PHIIn = BCPN->getIncomingValueForBlock(PredBB);
+    
+    // Otherwise insert a bitcast at the end of PredBB.
+    return new BitCastInst(PHIIn, InVal->getType(),
+                           InVal->getName()+".phi.trans.insert",
+                           PredBB->getTerminator());
+  }
+  
+  // Handle getelementptr with at least one PHI operand.
+  if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
+    SmallVector<Value*, 8> GEPOps;
+    Value *APHIOp = 0;
+    BasicBlock *CurBB = GEP->getParent();
+    for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
+      GEPOps.push_back(GEP->getOperand(i)->DoPHITranslation(CurBB, PredBB));
+      if (!isa<Constant>(GEPOps.back()))
+        APHIOp = GEPOps.back();
+    }
+    
+    GetElementPtrInst *Result = 
+      GetElementPtrInst::Create(GEPOps[0], GEPOps.begin()+1, GEPOps.end(),
+                                InVal->getName()+".phi.trans.insert",
+                                PredBB->getTerminator());
+    Result->setIsInBounds(GEP->isInBounds());
+    return Result;
+  }
+  
+  return 0;
+}
 
 /// getNonLocalPointerDepFromBB - Perform a dependency query based on
 /// pointer/pointeesize starting at the end of StartBB.  Add any clobber/def
-- 
cgit v1.2.3