[llvm] x86: fix musttail sibcall miscompilation (PR #168956)

[Folkert de Vries via llvm-commits]

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@@ -2943,26 +3078,6 @@ bool X86TargetLowering::IsEligibleForTailCallOptimization(
   // If the callee takes no arguments then go on to check the results of the
   // call.
   if (!Outs.empty()) {
-    if (StackArgsSize > 0) {
-      // Check if the arguments are already laid out in the right way as
-      // the caller's fixed stack objects.
-      MachineFrameInfo &MFI = MF.getFrameInfo();
-      const MachineRegisterInfo *MRI = &MF.getRegInfo();
-      const X86InstrInfo *TII = Subtarget.getInstrInfo();
-      for (unsigned I = 0, E = ArgLocs.size(); I != E; ++I) {
-        const CCValAssign &VA = ArgLocs[I];
-        SDValue Arg = OutVals[I];
-        ISD::ArgFlagsTy Flags = Outs[I].Flags;
-        if (VA.getLocInfo() == CCValAssign::Indirect)
-          return false;
-        if (!VA.isRegLoc()) {
-          if (!MatchingStackOffset(Arg, VA.getLocMemOffset(), Flags, MFI, MRI,
-                                   TII, VA))
-            return false;
-        }
-      }
-    }
-
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folkertdev wrote:

This rejected tail calls that needed stack shuffling, but because we handle that logic now, this restriction can be removed.

https://github.com/llvm/llvm-project/pull/168956