[OpaquePtrs][Clang] Add -opaque-pointers/-no-opaque-pointers cc1 options

[nikic]

Summary

This adds cc1 options for enabling and disabling opaque pointers on the clang side. This is not super useful now (because -mllvm -opaque-pointers and -Xclang -opaque-pointers have the same visible effect) but will be important once opaque pointers are enabled by default in clang. In that case, it will only be possible to disable them using the cc1 -no-opaque-pointers option.

[dblaikie]

Sounds good to me

clang/include/clang/Basic/CodeGenOptions.def

 
 /// Whether to skip RAX setup when passing variable arguments (x86 only).
 CODEGENOPT(SkipRaxSetup, 1, 0)
 
 /// Whether to zero out caller-used registers before returning.
 ENUM_CODEGENOPT(ZeroCallUsedRegs, llvm::ZeroCallUsedRegs::ZeroCallUsedRegsKind,
                 5, llvm::ZeroCallUsedRegs::ZeroCallUsedRegsKind::Skip)
 
+/// Whether to use opaque pointers.
+CODEGENOPT(OpaquePointers, 1, 0)
+
 #undef CODEGENOPT
 #undef ENUM_CODEGENOPT
 #undef VALUE_CODEGENOPT

clang/include/clang/Driver/Options.td

defm clear_ast_before_backend : BoolOption<"",
   BothFlags<[], " the Clang AST before running backend code generation">>;
 defm enable_noundef_analysis : BoolOption<"",
   "enable-noundef-analysis",
   CodeGenOpts<"EnableNoundefAttrs">,
   DefaultTrue,
   PosFlag<SetTrue, [], "Enable">,
   NegFlag<SetFalse, [], "Disable">,
   BothFlags<[], " analyzing function argument and return types for mandatory definedness">>;
+defm opaque_pointers : BoolOption<"",
+  "opaque-pointers",
+  CodeGenOpts<"OpaquePointers">,
+  DefaultFalse,
+  PosFlag<SetTrue, [], "Enable">,
+  NegFlag<SetFalse, [], "Disable">,
+  BothFlags<[], " opaque pointers">>;
 def discard_value_names : Flag<["-"], "discard-value-names">,
   HelpText<"Discard value names in LLVM IR">,
   MarshallingInfoFlag<CodeGenOpts<"DiscardValueNames">>;
 def plugin_arg : JoinedAndSeparate<["-"], "plugin-arg-">,
     MetaVarName<"<name> <arg>">,
     HelpText<"Pass <arg> to plugin <name>">;
 def add_plugin : Separate<["-"], "add-plugin">, MetaVarName<"<name>">,
   HelpText<"Use the named plugin action in addition to the default action">,

clang/lib/CodeGen/CodeGenAction.cpp

CodeGenAction::CreateASTConsumer(CompilerInstance &CI, StringRef InFile) {
   BackendAction BA = static_cast<BackendAction>(Act);
   std::unique_ptr<raw_pwrite_stream> OS = CI.takeOutputStream();
   if (!OS)
     OS = GetOutputStream(CI, InFile, BA);
 
   if (BA != Backend_EmitNothing && !OS)
     return nullptr;
 
+  if (CI.getCodeGenOpts().OpaquePointers)
+    VMContext->enableOpaquePointers();
+
   // Load bitcode modules to link with, if we need to.
   if (LinkModules.empty())
     for (const CodeGenOptions::BitcodeFileToLink &F :
          CI.getCodeGenOpts().LinkBitcodeFiles) {
       auto BCBuf = CI.getFileManager().getBufferForFile(F.Filename);
       if (!BCBuf) {
         CI.getDiagnostics().Report(diag::err_cannot_open_file)
             << F.Filename << BCBuf.getError().message();

clang/test/CodeGen/opaque-pointers-flag.c

+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py
+// RUN: %clang_cc1 -no-opaque-pointers -triple x86_64-unknown-unknown -emit-llvm %s -o - | FileCheck %s -check-prefix=TYPED
+// RUN: %clang_cc1 -opaque-pointers -triple x86_64-unknown-unknown -emit-llvm %s -o - | FileCheck %s -check-prefix=OPAQUE
+// The current default is typed pointers:
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm %s -o - | FileCheck %s -check-prefix=TYPED
+
+// TYPED-LABEL: @test(
+// TYPED-NEXT:  entry:
+// TYPED-NEXT:    [[P_ADDR:%.*]] = alloca i32*, align 8
+// TYPED-NEXT:    store i32* [[P:%.*]], i32** [[P_ADDR]], align 8
+// TYPED-NEXT:    [[TMP0:%.*]] = load i32*, i32** [[P_ADDR]], align 8
+// TYPED-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds i32, i32* [[TMP0]], i64 1
+// TYPED-NEXT:    [[TMP1:%.*]] = load i32, i32* [[ARRAYIDX]], align 4
+// TYPED-NEXT:    ret i32 [[TMP1]]
+//
+// OPAQUE-LABEL: @test(
+// OPAQUE-NEXT:  entry:
+// OPAQUE-NEXT:    [[P_ADDR:%.*]] = alloca ptr, align 8
+// OPAQUE-NEXT:    store ptr [[P:%.*]], ptr [[P_ADDR]], align 8
+// OPAQUE-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[P_ADDR]], align 8
+// OPAQUE-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds i32, ptr [[TMP0]], i64 1
+// OPAQUE-NEXT:    [[TMP1:%.*]] = load i32, ptr [[ARRAYIDX]], align 4
+// OPAQUE-NEXT:    ret i32 [[TMP1]]
+//
+int test(int *p) {
+  return p[1];
+}