[lanai] Add back the ability to set the memory model with --mcmodel. (#150575)

This ability got removed at some point but is still needed to select specific modes for Lanai backend. Add back with simple frontend smoke test.

Author: petergrind3

clang/docs/ReleaseNotes.rst

@@ -147,6 +147,10 @@ New Compiler Flags
 ------------------
 - New option ``-fno-sanitize-annotate-debug-info-traps`` added to disable emitting trap reasons into the debug info when compiling with trapping UBSan (e.g. ``-fsanitize-trap=undefined``).
 
+Lanai Support
+^^^^^^^^^^^^^^
+- The option ``-mcmodel={small,medium,large}`` is supported again.
+
 Deprecated Compiler Flags
 -------------------------
 

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -3125,6 +3125,8 @@ void tools::addMCModel(const Driver &D, const llvm::opt::ArgList &Args,
       else if (CM == "medany")
         CM = "large";
       Ok = CM == "small" || CM == "medium" || CM == "large";
+    } else if (Triple.getArch() == llvm::Triple::lanai) {
+      Ok = llvm::is_contained({"small", "medium", "large"}, CM);
     }
     if (Ok) {
       CmdArgs.push_back(Args.MakeArgString("-mcmodel=" + CM));

clang/test/Driver/lanai-mcmodel.c

@@ -0,0 +1,10 @@
+// RUN: %clang --target=lanai -### -c -mcmodel=small %s 2>&1 | FileCheck --check-prefix=SMALL %s
+// RUN: %clang --target=lanai -### -c -mcmodel=medium %s 2>&1 | FileCheck --check-prefix=MEDIUM %s
+// RUN: %clang --target=lanai -### -c -mcmodel=large %s 2>&1 | FileCheck --check-prefix=LARGE %s
+// RUN: not %clang --target=lanai -### -c -mcmodel=something %s 2>&1 | FileCheck --check-prefix=ERR-MCMODEL %s
+
+// SMALL: "-mcmodel=small"
+// MEDIUM: "-mcmodel=medium"
+// LARGE: "-mcmodel=large"
+
+// ERR-MCMODEL:  error: unsupported argument 'something' to option '-mcmodel=' for target 'lanai'