Add flag to request Clang is ABI-compatible with older versions of itself

This patch adds a flag -fclang-abi-compat that can be used to request that
Clang attempts to be ABI-compatible with some older version of itself.

This is provided on a best-effort basis; right now, this can be used to undo
the ABI change in r310401, reverting Clang to its prior C++ ABI for pass/return
by value of class types affected by that change, and to undo the ABI change in
r262688, reverting Clang to using integer registers rather than SSE registers
for passing <1 x long long> vectors. The intent is that we will maintain this
backwards compatibility path as we make ABI-breaking fixes in future.

The reversion to the old behavior for r310401 is also applied to the PS4 target
since that change is not part of its platform ABI (which is essentially to do
whatever Clang 3.2 did).

llvm-svn: 311823

7 files changed, 62 insertions, 5 deletions

diff --git a/clang/lib/CodeGen/ABIInfo.h b/clang/lib/CodeGen/ABIInfo.h
index e4dce2f2a00..575506da84d 100644
--- a/clang/lib/CodeGen/ABIInfo.h
+++ b/clang/lib/CodeGen/ABIInfo.h
@@ -24,6 +24,7 @@ namespace llvm {
 
 namespace clang {
   class ASTContext;
+  class CodeGenOptions;
   class TargetInfo;
 
 namespace CodeGen {
@@ -68,6 +69,7 @@ namespace swiftcall {
     llvm::LLVMContext &getVMContext() const;
     const llvm::DataLayout &getDataLayout() const;
     const TargetInfo &getTarget() const;
+    const CodeGenOptions &getCodeGenOpts() const;
 
     /// Return the calling convention to use for system runtime
     /// functions.
diff --git a/clang/lib/CodeGen/CodeGenTypes.cpp b/clang/lib/CodeGen/CodeGenTypes.cpp
index 4ba0ba863c9..adc3b9b4c83 100644
--- a/clang/lib/CodeGen/CodeGenTypes.cpp
+++ b/clang/lib/CodeGen/CodeGenTypes.cpp
@@ -44,6 +44,10 @@ CodeGenTypes::~CodeGenTypes() {
     delete &*I++;
 }
 
+const CodeGenOptions &CodeGenTypes::getCodeGenOpts() const {
+  return CGM.getCodeGenOpts();
+}
+
 void CodeGenTypes::addRecordTypeName(const RecordDecl *RD,
                                      llvm::StructType *Ty,
                                      StringRef suffix) {
diff --git a/clang/lib/CodeGen/CodeGenTypes.h b/clang/lib/CodeGen/CodeGenTypes.h
index f0b97ebde1c..9d0e3ded23e 100644
--- a/clang/lib/CodeGen/CodeGenTypes.h
+++ b/clang/lib/CodeGen/CodeGenTypes.h
@@ -178,6 +178,7 @@ public:
   const TargetInfo &getTarget() const { return Target; }
   CGCXXABI &getCXXABI() const { return TheCXXABI; }
   llvm::LLVMContext &getLLVMContext() { return TheModule.getContext(); }
+  const CodeGenOptions &getCodeGenOpts() const;
 
   /// ConvertType - Convert type T into a llvm::Type.
   llvm::Type *ConvertType(QualType T);
diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index 5c33f8c1afa..d78c032cec8 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -62,9 +62,20 @@ public:
 
   bool classifyReturnType(CGFunctionInfo &FI) const override;
 
+  bool passClassIndirect(const CXXRecordDecl *RD) const {
+    // Clang <= 4 used the pre-C++11 rule, which ignores move operations.
+    // The PS4 platform ABI follows the behavior of Clang 3.2.
+    if (CGM.getCodeGenOpts().getClangABICompat() <=
+            CodeGenOptions::ClangABI::Ver4 ||
+        CGM.getTriple().getOS() == llvm::Triple::PS4)
+      return RD->hasNonTrivialDestructor() ||
+             RD->hasNonTrivialCopyConstructor();
+    return !canCopyArgument(RD);
+  }
+
   RecordArgABI getRecordArgABI(const CXXRecordDecl *RD) const override {
     // If C++ prohibits us from making a copy, pass by address.
-    if (!canCopyArgument(RD))
+    if (passClassIndirect(RD))
       return RAA_Indirect;
     return RAA_Default;
   }
@@ -1012,7 +1023,7 @@ bool ItaniumCXXABI::classifyReturnType(CGFunctionInfo &FI) const {
     return false;
 
   // If C++ prohibits us from making a copy, return by address.
-  if (!canCopyArgument(RD)) {
+  if (passClassIndirect(RD)) {
     auto Align = CGM.getContext().getTypeAlignInChars(FI.getReturnType());
     FI.getReturnInfo() = ABIArgInfo::getIndirect(Align, /*ByVal=*/false);
     return true;
diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index 64ee31f83d3..77b9b4caab5 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -184,7 +184,11 @@ const TargetInfo &ABIInfo::getTarget() const {
   return CGT.getTarget();
 }
 
-bool ABIInfo:: isAndroid() const { return getTarget().getTriple().isAndroid(); }
+const CodeGenOptions &ABIInfo::getCodeGenOpts() const {
+  return CGT.getCodeGenOpts();
+}
+
+bool ABIInfo::isAndroid() const { return getTarget().getTriple().isAndroid(); }
 
 bool ABIInfo::isHomogeneousAggregateBaseType(QualType Ty) const {
   return false;
@@ -2112,9 +2116,14 @@ class X86_64ABIInfo : public SwiftABIInfo {
     return !getTarget().getTriple().isOSDarwin();
   }
 
-  /// GCC classifies <1 x long long> as SSE but compatibility with older clang
-  // compilers require us to classify it as INTEGER.
+  /// GCC classifies <1 x long long> as SSE but some platform ABIs choose to
+  /// classify it as INTEGER (for compatibility with older clang compilers).
   bool classifyIntegerMMXAsSSE() const {
+    // Clang <= 3.8 did not do this.
+    if (getCodeGenOpts().getClangABICompat() <=
+        CodeGenOptions::ClangABI::Ver3_8)
+      return false;
+
     const llvm::Triple &Triple = getTarget().getTriple();
     if (Triple.isOSDarwin() || Triple.getOS() == llvm::Triple::PS4)
       return false;
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index fa768b70c53..47b9256f6c4 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2933,6 +2933,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
 
   addPGOAndCoverageFlags(C, D, Output, Args, CmdArgs);
 
+  if (auto *ABICompatArg = Args.getLastArg(options::OPT_fclang_abi_compat_EQ))
+    ABICompatArg->render(Args, CmdArgs);
+
   // Add runtime flag for PS4 when PGO or Coverage are enabled.
   if (getToolChain().getTriple().isPS4CPU())
     PS4cpu::addProfileRTArgs(getToolChain(), Args, CmdArgs);
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index aea3af98285..abf6b0b302f 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -573,6 +573,33 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   if (!Opts.ProfileInstrumentUsePath.empty())
     setPGOUseInstrumentor(Opts, Opts.ProfileInstrumentUsePath);
 
+  if (Arg *A = Args.getLastArg(OPT_fclang_abi_compat_EQ)) {
+    Opts.setClangABICompat(CodeGenOptions::ClangABI::Latest);
+
+    StringRef Ver = A->getValue();
+    std::pair<StringRef, StringRef> VerParts = Ver.split('.');
+    unsigned Major, Minor = 0;
+
+    // Check the version number is valid: either 3.x (0 <= x <= 9) or
+    // y or y.0 (4 <= y <= current version).
+    if (!VerParts.first.startswith("0") &&
+        !VerParts.first.getAsInteger(10, Major) &&
+        3 <= Major && Major <= CLANG_VERSION_MAJOR &&
+        (Major == 3 ? VerParts.second.size() == 1 &&
+                      !VerParts.second.getAsInteger(10, Minor)
+                    : VerParts.first.size() == Ver.size() ||
+                      VerParts.second == "0")) {
+      // Got a valid version number.
+      if (Major == 3 && Minor <= 8)
+        Opts.setClangABICompat(CodeGenOptions::ClangABI::Ver3_8);
+      else if (Major <= 4)
+        Opts.setClangABICompat(CodeGenOptions::ClangABI::Ver4);
+    } else if (Ver != "latest") {
+      Diags.Report(diag::err_drv_invalid_value)
+          << A->getAsString(Args) << A->getValue();
+    }
+  }
+
   Opts.CoverageMapping =
       Args.hasFlag(OPT_fcoverage_mapping, OPT_fno_coverage_mapping, false);
   Opts.DumpCoverageMapping = Args.hasArg(OPT_dump_coverage_mapping);