Add option to enable global-isel on arm64 archs

LLVM will eventually switch over to using global-isel on arm64 archs.
Setting this option (SWIFT_ENABLE_GLOBAL_ISEL_ARM64) can be used to experiment
with that in Swift before the switch happens.

CMakeLists.txt

@@ -439,6 +439,10 @@ option(SWIFT_ENABLE_DISPATCH
   "Enable use of libdispatch"
   TRUE)
 
+option(SWIFT_ENABLE_GLOBAL_ISEL_ARM64
+  "Enable global isel on arm64, arm64e, arm64_32"
+  FALSE)
+
 cmake_dependent_option(SWIFT_BUILD_SYNTAXPARSERLIB
   "Build the Swift Syntax Parser library" TRUE
   "SWIFT_ENABLE_DISPATCH" FALSE)

include/swift/AST/IRGenOptions.h

@@ -343,6 +343,8 @@ public:
   /// Whether to disable using mangled names for accessing concrete type metadata.
   unsigned DisableConcreteTypeMetadataMangledNameAccessors : 1;
 
+  unsigned EnableGlobalISel : 1;
+
   /// The number of threads for multi-threaded code generation.
   unsigned NumThreads = 0;
 
@@ -396,7 +398,8 @@ public:
         UseTypeLayoutValueHandling(true),
         GenerateProfile(false), EnableDynamicReplacementChaining(false),
         DisableRoundTripDebugTypes(false), DisableDebuggerShadowCopies(false),
-        DisableConcreteTypeMetadataMangledNameAccessors(false), CmdArgs(),
+        DisableConcreteTypeMetadataMangledNameAccessors(false),
+        EnableGlobalISel(false), CmdArgs(),
         SanitizeCoverage(llvm::SanitizerCoverageOptions()),
         TypeInfoFilter(TypeInfoDumpFilter::All) {}
 

include/swift/Config.h.in

@@ -12,4 +12,6 @@
 
 #cmakedefine01 SWIFT_ENABLE_EXPERIMENTAL_DISTRIBUTED
 
+#cmakedefine01 SWIFT_ENABLE_GLOBAL_ISEL_ARM64
+
 #endif // SWIFT_CONFIG_H

lib/Frontend/CompilerInvocation.cpp

@@ -1873,6 +1873,12 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
     }
   }
 
+  if (SWIFT_ENABLE_GLOBAL_ISEL_ARM64 &&
+      (Triple.getArch() == llvm::Triple::aarch64 ||
+       Triple.getArch() == llvm::Triple::aarch64_32)) {
+    Opts.EnableGlobalISel = true;
+  }
+
   return false;
 }
 

lib/IRGen/IRGen.cpp

@@ -175,6 +175,9 @@ swift::getIRTargetOptions(const IRGenOptions &Opts, ASTContext &Ctx) {
   if (Clang->getTargetInfo().getTriple().isOSBinFormatWasm())
     TargetOpts.ThreadModel = llvm::ThreadModel::Single;
 
+  if (Opts.EnableGlobalISel)
+    TargetOpts.EnableGlobalISel = true;
+
   clang::TargetOptions &ClangOpts = Clang->getTargetInfo().getTargetOpts();
   return std::make_tuple(TargetOpts, ClangOpts.CPU, ClangOpts.Features, ClangOpts.Triple);
 }

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -138,6 +138,14 @@ function(_add_target_variant_c_compile_flags)
 
   set(result ${${CFLAGS_RESULT_VAR_NAME}})
 
+  if ("${CFLAGS_ARCH}" STREQUAL "arm64" OR
+      "${CFLAGS_ARCH}" STREQUAL "arm64e" OR
+      "${CFLAGS_ARCH}" STREQUAL "arm64_32")
+    if (SWIFT_ENABLE_GLOBAL_ISEL_ARM64)
+      list(APPEND result "-fglobal-isel")
+    endif()
+  endif()
+
   _add_target_variant_c_compile_link_flags(
     SDK "${CFLAGS_SDK}"
     ARCH "${CFLAGS_ARCH}"