[MachineOutliner][X86] Use TAILJMPd64 instead of JMP_1 for TailCall construction

[thegameg]

Summary

The machine verifier asserts with:

Assertion failed: (isMBB() && "Wrong MachineOperand accessor"), function getMBB, file ../include/llvm/CodeGen/MachineOperand.h, line 542.

It calls analyzeBranch which tries to call getMBB if the opcode is JMP_1, but in this case we do:

JMP_1 @OUTLINED_FUNCTION

I believe we have to use TAILJMPd64 instead of JMP_1 since JMP_1 is used with brtarget8.

[craig.topper]

This seems right to me. I assume from the use of CALL64pcrel32 in the other branch that outlining is 64-bit only?

[paquette]

This looks good to me.

In D49299#1161671, @craig.topper wrote:

This seems right to me. I assume from the use of CALL64pcrel32 in the other branch that outlining is 64-bit only?

Yep!

[craig.topper]

Though JMP_1 has a one byte offset and will get relaxed to JMP_4 by the assembler if the offset isn't in the range [128,-127]. TAILJMPd64 always encodes to the same encoding as JMP_4 and doesn't go through relaxation in the assembler.

I don't know enough about outlining. Are we usually/often getting a size savings from the JMP_1?

llvm/trunk/lib/Target/X86/X86InstrInfo.cpp

 X86InstrInfo::insertOutlinedCall(Module &M, MachineBasicBlock &MBB,
                                  MachineBasicBlock::iterator &It,
                                  MachineFunction &MF,
                                  const outliner::Candidate &C) const {
   // Is it a tail call?
   if (C.CallConstructionID == MachineOutlinerTailCall) {
     // Yes, just insert a JMP.
     It = MBB.insert(It,
-                  BuildMI(MF, DebugLoc(), get(X86::JMP_1))
+                  BuildMI(MF, DebugLoc(), get(X86::TAILJMPd64))
                       .addGlobalAddress(M.getNamedValue(MF.getName())));
   } else {
     // No, insert a call.
     It = MBB.insert(It,
                   BuildMI(MF, DebugLoc(), get(X86::CALL64pcrel32))
                       .addGlobalAddress(M.getNamedValue(MF.getName())));
   }
 
   return It;
 }

llvm/trunk/test/CodeGen/X86/machine-outliner-tailcalls.ll

-; RUN: llc -enable-machine-outliner -mtriple=x86_64-apple-darwin < %s | FileCheck %s
+; RUN: llc -verify-machineinstrs -enable-machine-outliner -mtriple=x86_64-apple-darwin < %s | FileCheck %s
 
 @x = common local_unnamed_addr global i32 0, align 4
 
 define i32 @foo0(i32) local_unnamed_addr #0 {
 ; CHECK-LABEL: _foo0:
 ; CHECK: jmp
 ; CHECK-SAME: OUTLINED_FUNCTION_0
 ; CHECK-NEXT: .cfi_endproc