Fix PR7328: when turning a tail recursion into a loop, need to preserve

the returned value after the tail call if it differs from other return
values.  The optimal thing to do would be to introduce a phi node for
the return value, but for the moment just fix the miscompile.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106947 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 23 insertions, 6 deletions

diff --git a/lib/Transforms/Scalar/TailRecursionElimination.cpp b/lib/Transforms/Scalar/TailRecursionElimination.cpp
index 42f4a5f71d..97e53e23d2 100644
--- a/lib/Transforms/Scalar/TailRecursionElimination.cpp
+++ b/lib/Transforms/Scalar/TailRecursionElimination.cpp
@@ -270,16 +270,16 @@ static bool isDynamicConstant(Value *V, CallInst *CI, ReturnInst *RI) {
 }
 
 // getCommonReturnValue - Check to see if the function containing the specified
-// return instruction and tail call consistently returns the same
-// runtime-constant value at all exit points.  If so, return the returned value.
+// tail call consistently returns the same runtime-constant value at all exit
+// points except for IgnoreRI.  If so, return the returned value.
 //
-static Value *getCommonReturnValue(ReturnInst *TheRI, CallInst *CI) {
-  Function *F = TheRI->getParent()->getParent();
+static Value *getCommonReturnValue(ReturnInst *IgnoreRI, CallInst *CI) {
+  Function *F = CI->getParent()->getParent();
   Value *ReturnedValue = 0;
 
   for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI)
     if (ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator()))
-      if (RI != TheRI) {
+      if (RI != IgnoreRI) {
         Value *RetOp = RI->getOperand(0);
 
         // We can only perform this transformation if the value returned is
@@ -404,7 +404,7 @@ bool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry,
   if (Ret->getNumOperands() == 1 && Ret->getReturnValue() != CI &&
       !isa<UndefValue>(Ret->getReturnValue()) &&
       AccumulatorRecursionEliminationInitVal == 0 &&
-      !getCommonReturnValue(Ret, CI))
+      !getCommonReturnValue(0, CI))
     return false;
 
   // OK! We can transform this tail call.  If this is the first one found,
diff --git a/test/Transforms/TailCallElim/2010-06-26-MultipleReturnValues.ll b/test/Transforms/TailCallElim/2010-06-26-MultipleReturnValues.ll
new file mode 100644
index 0000000000..f39476f7da
--- /dev/null
+++ b/test/Transforms/TailCallElim/2010-06-26-MultipleReturnValues.ll
@@ -0,0 +1,17 @@
+; RUN: opt < %s -tailcallelim -S | FileCheck %s
+; PR7328
+define i32 @foo(i32 %x) {
+; CHECK: define i32 @foo
+entry:
+  %cond = icmp ugt i32 %x, 0                      ; <i1> [#uses=1]
+  br i1 %cond, label %return, label %body
+
+body:                                             ; preds = %entry
+  %y = add i32 %x, 1                              ; <i32> [#uses=1]
+  %tmp = call i32 @foo(i32 %y)                    ; <i32> [#uses=0]
+  ret i32 0
+; CHECK: ret i32 0
+
+return:                                           ; preds = %entry
+  ret i32 1
+}