[CodeGen][ARM64EC] Don't treat guest exit thunks as indirect calls

Guest exit thunks serve as glue for performing direct calls, so they shouldn’t treat the target as an indirect one.

Spotted by @coneco-cy in #165504.

Author: cjacek

llvm/lib/Target/AArch64/AArch64Arm64ECCallLowering.cpp

@@ -655,16 +655,10 @@ Function *AArch64Arm64ECCallLowering::buildGuestExitThunk(Function *F) {
   BasicBlock *BB = BasicBlock::Create(M->getContext(), "", GuestExit);
   IRBuilder<> B(BB);
 
-  // Load the global symbol as a pointer to the check function.
-  Value *GuardFn;
-  if (cfguard_module_flag == 2 && !F->hasFnAttribute("guard_nocf"))
-    GuardFn = GuardFnCFGlobal;
-  else
-    GuardFn = GuardFnGlobal;
-  LoadInst *GuardCheckLoad = B.CreateLoad(PtrTy, GuardFn);
-
-  // Create new call instruction. The CFGuard check should always be a call,
-  // even if the original CallBase is an Invoke or CallBr instruction.
+  // Create new call instruction. The call check should always be a call,
+  // even if the original CallBase is an Invoke or CallBr instructio.
+  // This is treated as a direct call, so do not use GuardFnCFGlobal.
+  LoadInst *GuardCheckLoad = B.CreateLoad(PtrTy, GuardFnGlobal);
   Function *Thunk = buildExitThunk(F->getFunctionType(), F->getAttributes());
   CallInst *GuardCheck = B.CreateCall(
       GuardFnType, GuardCheckLoad, {F, Thunk});

llvm/test/CodeGen/WinCFGuard/cfguard-arm64ec.ll

@@ -0,0 +1,89 @@
+; REQUIRES: aarch64-registered-target
+; RUN: llc < %s -mtriple=arm64ec-windows | FileCheck %s
+
+; This file was generated from the following source, using this command line:
+; clang -target arm64ec-windows cfguard-arm64ec.c -S -emit-llvm -o cfguard-arm64ec.ll -O -Xclang -cfguard
+;
+;-------------------------------------------------------------------------------
+; extern void ext(void);
+;
+; void func(void (*f)())
+; {
+;     ext();
+;     f();
+; }
+;-------------------------------------------------------------------------------
+
+; ModuleID = 'cfguard-arm64ec.c'
+source_filename = "cfguard-arm64ec.c"
+target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-p:64:64-i32:32-i64:64-i128:128-n32:64-S128-Fn32"
+target triple = "arm64ec-unknown-windows-msvc19.33.0"
+
+; CHECK: "@feat.00" = 2048
+
+; Function Attrs: nounwind uwtable
+define dso_local void @func(ptr noundef readonly captures(none) %f) local_unnamed_addr #0 {
+entry:
+  tail call void @ext() #2
+; CHECK:  bl   "#ext"
+  tail call void %f() #2
+; CHECK-NEXT:  adrp    x8, __os_arm64x_check_icall_cfg
+; CHECK-NEXT:  adrp    x10, $iexit_thunk$cdecl$v$v
+; CHECK-NEXT:  add     x10, x10, :lo12:$iexit_thunk$cdecl$v$v
+; CHECK-NEXT:  ldr     x8, [x8, :lo12:__os_arm64x_check_icall_cfg]
+; CHECK-NEXT:  mov     x11, x19
+; CHECK-NEXT:  blr     x8
+  ret void
+}
+
+declare dso_local void @ext() local_unnamed_addr #1
+
+; CHECK:              .def    "#ext$exit_thunk";
+; CHECK-NEXT:         .scl    2;
+; CHECK-NEXT:         .type   32;
+; CHECK-NEXT:         .endef
+; CHECK-NEXT:         .section        .wowthk$aa,"xr",discard,"#ext$exit_thunk"
+; CHECK-NEXT:         .globl  "#ext$exit_thunk"               // -- Begin function #ext$exit_thunk
+; CHECK-NEXT:         .p2align        2
+; CHECK-NEXT: "#ext$exit_thunk":                      // @"#ext$exit_thunk"
+; CHECK-NEXT:         .weak_anti_dep  ext
+; CHECK-NEXT: ext = "#ext"
+; CHECK-NEXT:         .weak_anti_dep  "#ext"
+; CHECK-NEXT: "#ext" = "#ext$exit_thunk"
+; CHECK-NEXT: .seh_proc "#ext$exit_thunk"
+; CHECK-NEXT: // %bb.0:
+; CHECK-NEXT:         str     x30, [sp, #-16]!                // 8-byte Folded Spill
+; CHECK-NEXT:         .seh_save_reg_x x30, 16
+; CHECK-NEXT:         .seh_endprologue
+; CHECK-NEXT:         adrp    x8, __os_arm64x_check_icall
+; CHECK-NEXT:         adrp    x11, ext
+; CHECK-NEXT:         add     x11, x11, :lo12:ext
+; CHECK-NEXT:         ldr     x8, [x8, :lo12:__os_arm64x_check_icall]
+; CHECK-NEXT:         adrp    x10, $iexit_thunk$cdecl$v$v
+; CHECK-NEXT:         add     x10, x10, :lo12:$iexit_thunk$cdecl$v$v
+; CHECK-NEXT:         blr     x8
+; CHECK-NEXT:         .seh_startepilogue
+; CHECK-NEXT:         ldr     x30, [sp], #16                  // 8-byte Folded Reload
+; CHECK-NEXT:         .seh_save_reg_x x30, 16
+; CHECK-NEXT:         .seh_endepilogue
+; CHECK-NEXT:         br      x11
+; CHECK-NEXT:         .seh_endfunclet
+; CHECK-NEXT:         .seh_endproc
+
+attributes #0 = { nounwind uwtable "frame-pointer"="reserved" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+fp-armv8,+neon,+v8a,-fmv" }
+attributes #1 = { "frame-pointer"="reserved" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+fp-armv8,+neon,+v8a,-fmv" }
+attributes #2 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5, !6, !7}
+!llvm.ident = !{!8}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang version 22.0.0git", isOptimized: true, runtimeVersion: 0, emissionKind: NoDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "cfguard-arm64ec.c", directory: "/home/jacek/vbox-shared")
+!2 = !{i32 2, !"cfguard", i32 2}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 2}
+!5 = !{i32 8, !"PIC Level", i32 2}
+!6 = !{i32 7, !"uwtable", i32 2}
+!7 = !{i32 7, !"frame-pointer", i32 3}
+!8 = !{!"clang version 22.0.0git"}