Function parameter corruption when using tail call optimization in Windows 64

[llvmbot]

Bugzilla Link	9010
Resolution	FIXED
Resolved on	Mar 09, 2011 05:16
Version	trunk
OS	Windows XP
Blocks	llvm/llvm-bugzilla-archive#9100
Attachments	.ll and generated .s file
Reporter	LLVM Bugzilla Contributor

Extended Description

Tail call optimization is erroneously applied in Windows 64.
As result stack area which contains function parameters is released (RSP is updated) before the call (replaced by jump in tail call optimization). It may cause to wrong function behavior. See attached .s example. Specifically these 3 lines may explain the problem:

lea R8, QWORD PTR [RSP + 32] ; using stack to for parameter storage
...
add RSP, 232 ;; Stack is freed and allocated parameter with it
jmp testcall # TAILCALL

Attached are .ll and .s file generated with latest llc.

The simple inlined fix is solves the problem.

Index: lib/Target/X86/X86ISelLowering.cpp

--- lib/Target/X86/X86ISelLowering.cpp (revision 2609)
+++ lib/Target/X86/X86ISelLowering.cpp (working copy)
@@ -2501,6 +2501,9 @@
SmallVector<CCValAssign, 16> ArgLocs;
CCState CCInfo(CalleeCC, isVarArg, getTargetMachine(),
ArgLocs, *DAG.getContext());

• if (Subtarget->isTargetWin64()) {

• CCInfo.AllocateStack(32, 8); 
  

• }
  CCInfo.AnalyzeCallOperands(Outs, CCAssignFnForNode(CalleeCC));
  if (CCInfo.getNextStackOffset()) {
  MachineFunction &MF = DAG.getMachineFunction();

[llvmbot]

Please refer to my patches! :D
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110110/114977.html

Even if my patches were applied, your example might not be emitted optimally.
I know my patch would be suboptimal.

Comments and additional patches are welcome!

[llvmbot]

Sorry, Nakamura, I didn't see it.
Obviously your patches will solve the bug.

Please refer to my patches! :D
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110110/114977.html
Even if my patches were applied, your example might not be emitted optimally.
I know my patch would be suboptimal.
Comments and additional patches are welcome!

[llvmbot]

It has been fixed in r124272 and around.

I close this. Suboptimal cases (eg. this might be tailcallable) will be filed as another issue.

Thank you.

[llvmbot]

mentioned in issue llvm/llvm-bugzilla-archive#9100