fix a bug exposed by moving SRoA earlier which caused a crash building kc++

llvm-svn: 85786

llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp

@@ -749,7 +749,12 @@ void PromoteMem2Reg::RewriteSingleStoreAlloca(AllocaInst *AI,
     }
     
     // Otherwise, we *can* safely rewrite this load.
-    LI->replaceAllUsesWith(OnlyStore->getOperand(0));
+    Value *ReplVal = OnlyStore->getOperand(0);
+    // If the replacement value is the load, this must occur in unreachable
+    // code.
+    if (ReplVal == LI)
+      ReplVal = UndefValue::get(LI->getType());
+    LI->replaceAllUsesWith(ReplVal);
     if (AST && isa<PointerType>(LI->getType()))
       AST->deleteValue(LI);
     LI->eraseFromParent();

llvm/test/Transforms/Mem2Reg/crash.ll

 ; RUN: opt < %s -mem2reg -S
 ; PR5023
 
-declare i32 @bar()
+declare i32 @test1f()
 
-define i32 @foo() {
+define i32 @test1() {
 entry:
   %whichFlag = alloca i32
-  %A = invoke i32 @bar()
+  %A = invoke i32 @test1f()
           to label %invcont2 unwind label %lpad86
 
 invcont2:
@@ -22,3 +22,20 @@ lpad86:
   
 }
 
+
+
+define i32 @test2() {
+entry:
+  %whichFlag = alloca i32
+  br label %bb15
+
+bb15:
+  %B = load i32* %whichFlag
+  ret i32 %B
+
+invcont2:
+  %C = load i32* %whichFlag
+  store i32 %C, i32* %whichFlag
+  br label %bb15
+}
+