fix PR5837 by having SSAUpdate reuse phi nodes for the

'GetValueInMiddleOfBlock' case, instead of inserting 
duplicates.

A similar fix is almost certainly needed by the machine-level
SSAUpdate implementation.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91820 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Utils/SSAUpdater.cpp

@@ -149,7 +149,29 @@ Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
   if (SingularValue != 0)
     return SingularValue;
 
-  // Otherwise, we do need a PHI: insert one now.
+  // Otherwise, we do need a PHI: check to see if we already have one available
+  // in this block that produces the right value.
+  if (isa<PHINode>(BB->begin())) {
+    DenseMap<BasicBlock*, Value*> ValueMapping(PredValues.begin(),
+                                               PredValues.end());
+    PHINode *SomePHI;
+    for (BasicBlock::iterator It = BB->begin();
+         (SomePHI = dyn_cast<PHINode>(It)); ++It) {
+      // Scan this phi to see if it is what we need.
+      bool Equal = true;
+      for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i)
+        if (ValueMapping[SomePHI->getIncomingBlock(i)] !=
+            SomePHI->getIncomingValue(i)) {
+          Equal = false;
+          break;
+        }
+         
+      if (Equal)
+        return SomePHI;
+    }
+  }
+  
+  // Ok, we have no way out, insert a new one now.
   PHINode *InsertedPHI = PHINode::Create(PrototypeValue->getType(),
                                          PrototypeValue->getName(),
                                          &BB->front());

test/Transforms/LoopRotate/phi-duplicate.ll

@@ -0,0 +1,35 @@
+; RUN: opt -S %s -loop-rotate | FileCheck %s
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target triple = "x86_64-apple-darwin10.0"
+
+; PR5837
+define void @test(i32 %N, double* %G) nounwind ssp {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.body, %entry
+  %j.0 = phi i64 [ 1, %entry ], [ %inc, %for.body ] ; <i64> [#uses=5]
+  %cmp = icmp slt i64 %j.0, 1000                  ; <i1> [#uses=1]
+  br i1 %cmp, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  %arrayidx = getelementptr inbounds double* %G, i64 %j.0 ; <double*> [#uses=1]
+  %tmp3 = load double* %arrayidx                  ; <double> [#uses=1]
+  %sub = sub i64 %j.0, 1                          ; <i64> [#uses=1]
+  %arrayidx6 = getelementptr inbounds double* %G, i64 %sub ; <double*> [#uses=1]
+  %tmp7 = load double* %arrayidx6                 ; <double> [#uses=1]
+  %add = fadd double %tmp3, %tmp7                 ; <double> [#uses=1]
+  %arrayidx10 = getelementptr inbounds double* %G, i64 %j.0 ; <double*> [#uses=1]
+  store double %add, double* %arrayidx10
+  %inc = add nsw i64 %j.0, 1                      ; <i64> [#uses=1]
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  ret void
+}
+; Should only end up with one phi.
+; CHECK: for.body:
+; CHECK-NEXT: %j.02 = phi i64
+; CHECK-NOT phi
+; CHECK: ret void
+