teach memdep to do trivial PHI translation of GEPs. More to

come.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89979 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 69 insertions, 2 deletions

diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index 780d73e..6bffca6 100644
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -697,7 +697,14 @@ static bool isPHITranslatable(Instruction *Inst) {
       if (PN->getParent() == BC->getParent())
         return true;
   
-  // TODO: GEP, ...
+  // We can translate a GEP that uses a PHI in the current block for at least
+  // one of its operands.
+  if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
+    for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i)
+      if (PHINode *PN = dyn_cast<PHINode>(GEP->getOperand(i)))
+        if (PN->getParent() == GEP->getParent())
+          return true;
+  }
 
   //   cerr << "MEMDEP: Could not PHI translate: " << *Pointer;
   //   if (isa<BitCastInst>(PtrInst) || isa<GetElementPtrInst>(PtrInst))
@@ -713,6 +720,7 @@ static Value *PHITranslateForPred(Instruction *Inst, BasicBlock *Pred) {
   if (PHINode *PN = dyn_cast<PHINode>(Inst))
     return PN->getIncomingValueForBlock(Pred);
   
+  // Handle bitcast of PHI.
   if (BitCastInst *BC = dyn_cast<BitCastInst>(Inst)) {
     PHINode *BCPN = cast<PHINode>(BC->getOperand(0));
     Value *PHIIn = BCPN->getIncomingValueForBlock(Pred);
@@ -732,6 +740,39 @@ static Value *PHITranslateForPred(Instruction *Inst, BasicBlock *Pred) {
     return 0;
   }
 
+  // Handle getelementptr with at least one PHI operand.
+  if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
+    SmallVector<Value*, 8> GEPOps;
+    Value *APHIOp = 0;
+    for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
+      GEPOps.push_back(GEP->getOperand(i));
+      if (PHINode *PN = dyn_cast<PHINode>(GEP->getOperand(i)))
+        if (PN->getParent() == GEP->getParent())
+          GEPOps.back() = APHIOp = PN->getIncomingValueForBlock(Pred);
+    }
+    
+    // TODO: Simplify the GEP to handle 'gep x, 0' -> x etc.
+    
+    // Scan to see if we have this GEP available.
+    for (Value::use_iterator UI = APHIOp->use_begin(), E = APHIOp->use_end();
+         UI != E; ++UI) {
+      if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI))
+        if (GEPI->getType() == GEPI->getType() &&
+            GEPI->getNumOperands() == GEPOps.size() &&
+            GEPI->getParent()->getParent() == Inst->getParent()->getParent()) {
+          bool Mismatch = false;
+          for (unsigned i = 0, e = GEPOps.size(); i != e; ++i)
+            if (GEPI->getOperand(i) != GEPOps[i]) {
+              Mismatch = true;
+              break;
+            }
+          if (!Mismatch)
+            return GEPI;
+        }
+    }
+    return 0;
+  }
+  
   return 0;
 }
 
diff --git a/test/Transforms/GVN/rle-phi-translate.ll b/test/Transforms/GVN/rle-phi-translate.ll
index 89f5ac3..ac9e7aa 100644
--- a/test/Transforms/GVN/rle-phi-translate.ll
+++ b/test/Transforms/GVN/rle-phi-translate.ll
@@ -54,9 +54,35 @@ bb2:
 	%d = phi i32* [ %c, %bb1 ], [ %b, %bb ]
   %d1 = bitcast i32* %d to i8*
 	%dv = load i8* %d1
-; CHECK: %dv = phi i8
+; CHECK: %dv = phi i8 [ 92, %bb1 ], [ 4, %bb ]
 ; CHECK-NOT: load
 ; CHECK: ret i8 %dv
 	ret i8 %dv
 }
 
+define i32 @test3(i1 %cond, i32* %b, i32* %c) nounwind {
+; CHECK: @test3
+entry:
+	br i1 %cond, label %bb, label %bb1
+
+bb:
+  %b1 = getelementptr i32* %b, i32 17
+  store i32 4, i32* %b1
+	br label %bb2
+
+bb1:
+  %c1 = getelementptr i32* %c, i32 7
+  store i32 82, i32* %c1
+	br label %bb2
+
+bb2:
+	%d = phi i32* [ %c, %bb1 ], [ %b, %bb ]
+	%i = phi i32 [ 7, %bb1 ], [ 17, %bb ]
+  %d1 = getelementptr i32* %d, i32 %i
+	%dv = load i32* %d1
+; CHECK: %dv = phi i32 [ 82, %bb1 ], [ 4, %bb ]
+; CHECK-NOT: load
+; CHECK: ret i32 %dv
+	ret i32 %dv
+}
+