[llvm][X86] REX profile for UEFI (#138362)

Use the appropriate REX prefix for UEFI X86_64 target.

Author: Prabhuk

llvm/lib/Target/X86/X86ExpandPseudo.cpp

@@ -301,8 +301,9 @@ bool X86ExpandPseudo::expandMI(MachineBasicBlock &MBB,
       X86FL->emitSPUpdate(MBB, MBBI, DL, Offset, /*InEpilogue=*/true);
     }
 
+    // Use this predicate to set REX prefix for X86_64 targets.
+    bool IsX64 = STI->isTargetWin64() || STI->isTargetUEFI64();
     // Jump to label or value in register.
-    bool IsWin64 = STI->isTargetWin64();
     if (Opcode == X86::TCRETURNdi || Opcode == X86::TCRETURNdicc ||
         Opcode == X86::TCRETURNdi64 || Opcode == X86::TCRETURNdi64cc) {
       unsigned Op;
@@ -341,18 +342,18 @@ bool X86ExpandPseudo::expandMI(MachineBasicBlock &MBB,
     } else if (Opcode == X86::TCRETURNmi || Opcode == X86::TCRETURNmi64) {
       unsigned Op = (Opcode == X86::TCRETURNmi)
                         ? X86::TAILJMPm
-                        : (IsWin64 ? X86::TAILJMPm64_REX : X86::TAILJMPm64);
+                        : (IsX64 ? X86::TAILJMPm64_REX : X86::TAILJMPm64);
       MachineInstrBuilder MIB = BuildMI(MBB, MBBI, DL, TII->get(Op));
       for (unsigned i = 0; i != X86::AddrNumOperands; ++i)
         MIB.add(MBBI->getOperand(i));
     } else if ((Opcode == X86::TCRETURNri64) ||
                (Opcode == X86::TCRETURNri64_ImpCall)) {
       JumpTarget.setIsKill();
       BuildMI(MBB, MBBI, DL,
-              TII->get(IsWin64 ? X86::TAILJMPr64_REX : X86::TAILJMPr64))
+              TII->get(IsX64 ? X86::TAILJMPr64_REX : X86::TAILJMPr64))
           .add(JumpTarget);
     } else {
-      assert(!IsWin64 && "Win64 requires REX for indirect jumps.");
+      assert(!IsX64 && "Win64 and UEFI64 require REX for indirect jumps.");
       JumpTarget.setIsKill();
       BuildMI(MBB, MBBI, DL, TII->get(X86::TAILJMPr))
           .add(JumpTarget);

llvm/test/CodeGen/X86/musttail-varargs.ll

@@ -2,6 +2,7 @@
 ; RUN: llc -verify-machineinstrs < %s -enable-tail-merge=0 -mtriple=x86_64-linux | FileCheck %s --check-prefix=LINUX
 ; RUN: llc -verify-machineinstrs < %s -enable-tail-merge=0 -mtriple=x86_64-linux-gnux32 | FileCheck %s --check-prefix=LINUX-X32
 ; RUN: llc -verify-machineinstrs < %s -enable-tail-merge=0 -mtriple=x86_64-windows | FileCheck %s --check-prefix=WINDOWS
+; RUN: llc -verify-machineinstrs < %s -enable-tail-merge=0 -mtriple=x86_64-uefi | FileCheck %s --check-prefix=WINDOWS
 ; RUN: llc -verify-machineinstrs < %s -enable-tail-merge=0 -mtriple=i686-windows | FileCheck %s --check-prefix=X86 --check-prefix=X86-NOSSE
 ; RUN: llc -verify-machineinstrs < %s -enable-tail-merge=0 -mtriple=i686-windows -mattr=+sse2 | FileCheck %s --check-prefix=X86 --check-prefix=X86-SSE
 

llvm/test/CodeGen/X86/rex-profile-test.ll

@@ -0,0 +1,18 @@
+;; Test that the UEFI and Windows targets set the rex64 correctly.
+; RUN: llc -mtriple x86_64-uefi %s -o - | FileCheck %s -check-prefix=REX
+; RUN: llc -mtriple x86_64-windows-msvc %s -o - | FileCheck %s -check-prefix=REX
+; RUN: llc -mtriple x86_64-unknown-linux %s -o - | FileCheck %s -check-prefix=NOREX
+
+define void @test_tailjmp(ptr %fptr) {
+; REX-LABEL:    test_tailjmp:           # @test_tailjmp
+; REX:          # %bb.0:                # %entry
+; REX-NEXT:     rex64   jmpq    *%rcx   # TAILCALL
+;
+; NOREX-LABEL:  test_tailjmp:           # @test_tailjmp
+; NOREX:        .cfi_startproc
+; NOREX-NEXT:   # %bb.0:                # %entry
+; NOREX-NEXT:   jmpq	*%rdi           # TAILCALL
+entry:
+  tail call void %fptr()
+  ret void
+}