[clang] [ARM64EC] Add support for parsing __vectorcall (PR #87725)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic created https://github.com/llvm/llvm-project/pull/87725

MSVC doesn't support generating __vectorcall calls in Arm64EC mode, but it does treat it as a distinct type.  The Microsoft STL depends on this functionality.  (Not sure if this is intentional.)  Add support for parsing the same way as MSVC, and add some checks to ensure we don't try to actually generate code.

The error handling in CodeGen is ugly, but I can't think of a better way to do it.

>From d9da9af25579e18dfe0b663fbddcf56a2a596d2d Mon Sep 17 00:00:00 2001
From: Eli Friedman <efriedma at quicinc.com>
Date: Thu, 4 Apr 2024 16:14:42 -0700
Subject: [PATCH] [ARM64EC] Add support for parsing __vectorcall

MSVC doesn't support generating __vectorcall calls in Arm64EC mode, but
it does treat it as a distinct type.  The Microsoft STL depends on this
functionality.  (Not sure if this is intentional.)  Add support for
parsing the same way as MSVC, and add some checks to ensure we don't
try to actually generate code.

The error handling in CodeGen is ugly, but I can't think of a better way
to do it.
---
 clang/lib/Basic/Targets/AArch64.cpp          |  5 ++++-
 clang/lib/CodeGen/CGCall.cpp                 |  6 ++++++
 clang/lib/CodeGen/CodeGenModule.cpp          |  8 ++++++++
 clang/test/CodeGenCXX/arm64ec-vectorcall.cpp | 14 ++++++++++++++
 4 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/CodeGenCXX/arm64ec-vectorcall.cpp

diff --git a/clang/lib/Basic/Targets/AArch64.cpp b/clang/lib/Basic/Targets/AArch64.cpp
index 1569b5e04b770a..c8d243a8fb7aea 100644
--- a/clang/lib/Basic/Targets/AArch64.cpp
+++ b/clang/lib/Basic/Targets/AArch64.cpp
@@ -1543,10 +1543,13 @@ WindowsARM64TargetInfo::getBuiltinVaListKind() const {
 TargetInfo::CallingConvCheckResult
 WindowsARM64TargetInfo::checkCallingConvention(CallingConv CC) const {
   switch (CC) {
+  case CC_X86VectorCall:
+    if (getTriple().isWindowsArm64EC())
+      return CCCR_OK;
+    return CCCR_Ignore;
   case CC_X86StdCall:
   case CC_X86ThisCall:
   case CC_X86FastCall:
-  case CC_X86VectorCall:
     return CCCR_Ignore;
   case CC_C:
   case CC_OpenCLKernel:
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index f12765b826935b..3f5463a9a70e9d 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -5591,6 +5591,12 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
                              /*AttrOnCallSite=*/true,
                              /*IsThunk=*/false);
 
+  if (CallingConv == llvm::CallingConv::X86_VectorCall &&
+      getTarget().getTriple().isWindowsArm64EC()) {
+    CGM.Error(Loc, "__vectorcall calling convention is not currently "
+                   "supported");
+  }
+
   if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(CurFuncDecl)) {
     if (FD->hasAttr<StrictFPAttr>())
       // All calls within a strictfp function are marked strictfp
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 00b3bfcaa0bc25..75519be8bba052 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -2087,6 +2087,14 @@ void CodeGenModule::SetLLVMFunctionAttributes(GlobalDecl GD,
   llvm::AttributeList PAL;
   ConstructAttributeList(F->getName(), Info, GD, PAL, CallingConv,
                          /*AttrOnCallSite=*/false, IsThunk);
+  if (CallingConv == llvm::CallingConv::X86_VectorCall &&
+      getTarget().getTriple().isWindowsArm64EC()) {
+    SourceLocation Loc;
+    if (const Decl *D = GD.getDecl())
+      Loc = D->getLocation();
+
+    Error(Loc, "__vectorcall calling convention is not currently supported");
+  }
   F->setAttributes(PAL);
   F->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));
 }
diff --git a/clang/test/CodeGenCXX/arm64ec-vectorcall.cpp b/clang/test/CodeGenCXX/arm64ec-vectorcall.cpp
new file mode 100644
index 00000000000000..73d2d63835917c
--- /dev/null
+++ b/clang/test/CodeGenCXX/arm64ec-vectorcall.cpp
@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -triple arm64ec-windows-msvc -emit-llvm -o - %s -verify
+
+// ARM64EC doesn't support generating __vectorcall calls... but __vectorcall
+// function types need to be distinct from __cdecl function types to support
+// compiling the STL. Make sure we only diagnose constructs that actually
+// require generating code.
+void __vectorcall f1();
+void f2(void __vectorcall p()) {}
+void f2(void p()) {}
+void __vectorcall (*f3)();
+void __vectorcall f4(); // expected-error {{__vectorcall}}
+void __vectorcall f5() { // expected-error {{__vectorcall}}
+  f4(); // expected-error{{__vectorcall}}
+}