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

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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
This commit is contained in:
Duncan Sands 2010-06-26 12:53:31 +00:00
parent 7a1d92a2cb
commit d50e9e2566
2 changed files with 23 additions and 6 deletions
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12
lib/Transforms/Scalar/TailRecursionElimination.cpp
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@ -270,16 +270,16 @@ static bool isDynamicConstant(Value *V, CallInst *CI, ReturnInst *RI) {
} }
// getCommonReturnValue - Check to see if the function containing the specified // getCommonReturnValue - Check to see if the function containing the specified
// return instruction and tail call consistently returns the same // tail call consistently returns the same runtime-constant value at all exit
// runtime-constant value at all exit points. If so, return the returned value. // points except for IgnoreRI. If so, return the returned value.
// //
static Value *getCommonReturnValue(ReturnInst *TheRI, CallInst *CI) { static Value *getCommonReturnValue(ReturnInst *IgnoreRI, CallInst *CI) {
Function *F = TheRI->getParent()->getParent(); Function *F = CI->getParent()->getParent();
Value *ReturnedValue = 0; Value *ReturnedValue = 0;
for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI) for (Function::iterator BBI = F->begin(), E = F->end(); BBI != E; ++BBI)
if (ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator())) if (ReturnInst *RI = dyn_cast<ReturnInst>(BBI->getTerminator()))
if (RI != TheRI) { if (RI != IgnoreRI) {
Value *RetOp = RI->getOperand(0); Value *RetOp = RI->getOperand(0);
// We can only perform this transformation if the value returned is // 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 && if (Ret->getNumOperands() == 1 && Ret->getReturnValue() != CI &&
!isa<UndefValue>(Ret->getReturnValue()) && !isa<UndefValue>(Ret->getReturnValue()) &&
AccumulatorRecursionEliminationInitVal == 0 && AccumulatorRecursionEliminationInitVal == 0 &&
!getCommonReturnValue(Ret, CI)) !getCommonReturnValue(0, CI))
return false; return false;
// OK! We can transform this tail call. If this is the first one found, // OK! We can transform this tail call. If this is the first one found,

17
test/Transforms/TailCallElim/2010-06-26-MultipleReturnValues.ll Normal file
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@ -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
}