CheckTailCallReturnConstraints is missing a check on the

incomming chain of the RETURN node. The incomming chain must
be the outgoing chain of the CALL node. This causes the
backend to identify tail calls that are not tail calls. This
patch fixes this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73387 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index ab4cd515531c42bc13ca8b3303073db00ca8022e..134a859cebd9e6eda11b01c647d62244724625b6 100644 (file)
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -2584,8 +2584,12 @@ bool TargetLowering::CheckTailCallReturnConstraints(CallSDNode *TheCall,
   // Check that operand of the RET node sources from the CALL node. The RET node
   // has at least two operands. Operand 0 holds the chain. Operand 1 holds the
   // value.
+  // Also we need to check that there is no code in between the call and the
+  // return. Hence we also check that the incomming chain to the return sources
+  // from the outgoing chain of the call.
   if (NumOps > 1 &&
-      IgnoreHarmlessInstructions(Ret.getOperand(1)) == SDValue(TheCall,0))
+      IgnoreHarmlessInstructions(Ret.getOperand(1)) == SDValue(TheCall,0) &&
+      Ret.getOperand(0) == SDValue(TheCall, TheCall->getNumValues()-1))
     return true;
   // void return: The RET node  has the chain result value of the CALL node as
   // input.

diff --git a/test/CodeGen/X86/2009-06-15-not-a-tail-call.ll b/test/CodeGen/X86/2009-06-15-not-a-tail-call.ll
new file mode 100644 (file)
index 0000000..095e6a1
--- /dev/null
+++ b/test/CodeGen/X86/2009-06-15-not-a-tail-call.ll
@@ -0,0 +1,14 @@
+; RUN: llvm-as < %s | llc -march=x86 -tailcallopt | not grep TAILCALL 
+
+; Bug 4396. This tail call can NOT be optimized.
+
+declare fastcc i8* @_D3gcx2GC12mallocNoSyncMFmkZPv() nounwind
+
+define fastcc i8* @_D3gcx2GC12callocNoSyncMFmkZPv() nounwind {
+entry:
+       %tmp6 = tail call fastcc i8* @_D3gcx2GC12mallocNoSyncMFmkZPv()          ; <i8*> [#uses=2]
+       %tmp9 = tail call i8* @memset(i8* %tmp6, i32 0, i64 2)          ; <i8*> [#uses=0]
+       ret i8* %tmp6
+}
+
+declare i8* @memset(i8*, i32, i64)