[flang] Add MSC_VER and target arch defines when targeting the MSVC ABI (#73250)

Fixes #67675

Author: DavidTruby

clang/lib/Driver/ToolChains/Flang.cpp

@@ -205,6 +205,30 @@ void Flang::AddAArch64TargetArgs(const ArgList &Args,
   }
 }
 
+static void addVSDefines(const ToolChain &TC, const ArgList &Args,
+                         ArgStringList &CmdArgs) {
+
+  unsigned ver = 0;
+  const VersionTuple vt = TC.computeMSVCVersion(nullptr, Args);
+  ver = vt.getMajor() * 10000000 + vt.getMinor().value_or(0) * 100000 +
+        vt.getSubminor().value_or(0);
+  CmdArgs.push_back(Args.MakeArgString("-D_MSC_VER=" + Twine(ver / 100000)));
+  CmdArgs.push_back(Args.MakeArgString("-D_MSC_FULL_VER=" + Twine(ver)));
+  CmdArgs.push_back(Args.MakeArgString("-D_WIN32"));
+
+  llvm::Triple triple = TC.getTriple();
+  if (triple.isAArch64()) {
+    CmdArgs.push_back("-D_M_ARM64=1");
+  } else if (triple.isX86() && triple.isArch32Bit()) {
+    CmdArgs.push_back("-D_M_IX86=600");
+  } else if (triple.isX86() && triple.isArch64Bit()) {
+    CmdArgs.push_back("-D_M_X64=100");
+  } else {
+    llvm_unreachable(
+        "Flang on Windows only supports X86_32, X86_64 and AArch64");
+  }
+}
+
 static void processVSRuntimeLibrary(const ToolChain &TC, const ArgList &Args,
                                     ArgStringList &CmdArgs) {
   assert(TC.getTriple().isKnownWindowsMSVCEnvironment() &&
@@ -334,6 +358,7 @@ void Flang::addTargetOptions(const ArgList &Args,
 
   if (Triple.isKnownWindowsMSVCEnvironment()) {
     processVSRuntimeLibrary(TC, Args, CmdArgs);
+    addVSDefines(TC, Args, CmdArgs);
   }
 
   // TODO: Add target specific flags, ABI, mtune option etc.

flang/test/Driver/msvc-defines.f90

@@ -0,0 +1,10 @@
+! RUN: %flang -### --target=aarch64-windows-msvc %S/Inputs/hello.f90 -v 2>&1 | FileCheck %s --check-prefixes=MSVC,MSVC-AARCH64
+! RUN: %flang -### --target=i386-windows-msvc %S/Inputs/hello.f90 -v 2>&1 | FileCheck %s --check-prefixes=MSVC,MSVC-X86_32
+! RUN: %flang -### --target=x86_64-windows-msvc %S/Inputs/hello.f90 -v 2>&1 | FileCheck %s --check-prefixes=MSVC,MSVC-X86_64
+
+! MSVC: -fc1
+! MSVC-SAME: -D_MSC_VER={{[0-9]*}}
+! MSVC-SAME: -D_MSC_FULL_VER={{[0-9]*}}
+! MSVC-AARCH64-SAME: -D_M_ARM64=1
+! MSVC-X86_32-SAME: -D_M_IX86=600
+! MSVC-X86_64-SAME: -D_M_X64=100