[PowerPC] Add clang -msvr4-struct-return for 32-bit ELF

Justin Hibbits · Justin Hibbits · commit 4ca2cad947d0 · 2020-04-21T20:17:25.000-05:00
Summary: Change the default ABI to be compatible with GCC. For 32-bit ELF targets other than Linux, Clang now returns small structs in registers r3/r4. This affects FreeBSD, NetBSD, OpenBSD. There is no change for 32-bit Linux, where Clang continues to return all structs in memory. Add clang options -maix-struct-return (to return structs in memory) and -msvr4-struct-return (to return structs in registers) to be compatible with gcc. These options are only for PPC32; reject them on PPC64 and other targets. The options are like -fpcc-struct-return and -freg-struct-return for X86_32, and use similar code. To actually return a struct in registers, coerce it to an integer of the same size. LLVM may optimize the code to remove unnecessary accesses to memory, and will return i32 in r3 or i64 in r3:r4. Fixes PR#40736 Patch by George Koehler! Reviewed By: jhibbits, nemanjai Differential Revision: https://reviews.llvm.org/D73290
diff --git a/clang/docs/ClangCommandLineReference.rst b/clang/docs/ClangCommandLineReference.rst
@@ -2973,6 +2973,11 @@ Enable MT ASE (MIPS only)
 
 PowerPC
 -------
+.. option:: -maix-struct-return
+
+Override the default ABI for 32-bit targets to return all structs in memory,
+as in the Power 32-bit ABI for Linux (2011), and on AIX and Darwin.
+
 .. option:: -maltivec, -mno-altivec
 
 .. option:: -mcmpb, -mno-cmpb
@@ -3009,6 +3014,11 @@ PowerPC
 
 .. option:: -mspe, -mno-spe
 
+.. option:: -msvr4-struct-return
+
+Override the default ABI for 32-bit targets to return small structs in
+registers, as in the System V ABI (1995).
+
 .. option:: -mvsx, -mno-vsx
 
 WebAssembly
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
@@ -2510,6 +2510,12 @@ def mlongcall: Flag<["-"], "mlongcall">,
     Group<m_ppc_Features_Group>;
 def mno_longcall : Flag<["-"], "mno-longcall">,
     Group<m_ppc_Features_Group>;
+def maix_struct_return : Flag<["-"], "maix-struct-return">,
+  Group<m_Group>, Flags<[CC1Option]>,
+  HelpText<"Return all structs in memory (PPC32 only)">;
+def msvr4_struct_return : Flag<["-"], "msvr4-struct-return">,
+  Group<m_Group>, Flags<[CC1Option]>,
+  HelpText<"Return small structs in registers (PPC32 only)">;
 
 def mvx : Flag<["-"], "mvx">, Group<m_Group>;
 def mno_vx : Flag<["-"], "mno-vx">, Group<m_Group>;
diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
@@ -4177,21 +4177,38 @@ namespace {
 /// PPC32_SVR4_ABIInfo - The 32-bit PowerPC ELF (SVR4) ABI information.
 class PPC32_SVR4_ABIInfo : public DefaultABIInfo {
   bool IsSoftFloatABI;
+  bool IsRetSmallStructInRegABI;
 
   CharUnits getParamTypeAlignment(QualType Ty) const;
 
 public:
-  PPC32_SVR4_ABIInfo(CodeGen::CodeGenTypes &CGT, bool SoftFloatABI)
-      : DefaultABIInfo(CGT), IsSoftFloatABI(SoftFloatABI) {}
+  PPC32_SVR4_ABIInfo(CodeGen::CodeGenTypes &CGT, bool SoftFloatABI,
+                     bool RetSmallStructInRegABI)
+      : DefaultABIInfo(CGT), IsSoftFloatABI(SoftFloatABI),
+        IsRetSmallStructInRegABI(RetSmallStructInRegABI) {}
+
+  ABIArgInfo classifyReturnType(QualType RetTy) const;
+
+  void computeInfo(CGFunctionInfo &FI) const override {
+    if (!getCXXABI().classifyReturnType(FI))
+      FI.getReturnInfo() = classifyReturnType(FI.getReturnType());
+    for (auto &I : FI.arguments())
+      I.info = classifyArgumentType(I.type);
+  }
 
   Address EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
                     QualType Ty) const override;
 };
 
 class PPC32TargetCodeGenInfo : public TargetCodeGenInfo {
 public:
-  PPC32TargetCodeGenInfo(CodeGenTypes &CGT, bool SoftFloatABI)
-      : TargetCodeGenInfo(new PPC32_SVR4_ABIInfo(CGT, SoftFloatABI)) {}
+  PPC32TargetCodeGenInfo(CodeGenTypes &CGT, bool SoftFloatABI,
+                         bool RetSmallStructInRegABI)
+      : TargetCodeGenInfo(new PPC32_SVR4_ABIInfo(CGT, SoftFloatABI,
+                                                 RetSmallStructInRegABI)) {}
+
+  static bool isStructReturnInRegABI(const llvm::Triple &Triple,
+                                     const CodeGenOptions &Opts);
 
   int getDwarfEHStackPointer(CodeGen::CodeGenModule &M) const override {
     // This is recovered from gcc output.
@@ -4227,6 +4244,34 @@ CharUnits PPC32_SVR4_ABIInfo::getParamTypeAlignment(QualType Ty) const {
   return CharUnits::fromQuantity(4);
 }
 
+ABIArgInfo PPC32_SVR4_ABIInfo::classifyReturnType(QualType RetTy) const {
+  uint64_t Size;
+
+  // -msvr4-struct-return puts small aggregates in GPR3 and GPR4.
+  if (isAggregateTypeForABI(RetTy) && IsRetSmallStructInRegABI &&
+      (Size = getContext().getTypeSize(RetTy)) <= 64) {
+    // System V ABI (1995), page 3-22, specified:
+    // > A structure or union whose size is less than or equal to 8 bytes
+    // > shall be returned in r3 and r4, as if it were first stored in the
+    // > 8-byte aligned memory area and then the low addressed word were
+    // > loaded into r3 and the high-addressed word into r4.  Bits beyond
+    // > the last member of the structure or union are not defined.
+    //
+    // GCC for big-endian PPC32 inserts the pad before the first member,
+    // not "beyond the last member" of the struct.  To stay compatible
+    // with GCC, we coerce the struct to an integer of the same size.
+    // LLVM will extend it and return i32 in r3, or i64 in r3:r4.
+    if (Size == 0)
+      return ABIArgInfo::getIgnore();
+    else {
+      llvm::Type *CoerceTy = llvm::Type::getIntNTy(getVMContext(), Size);
+      return ABIArgInfo::getDirect(CoerceTy);
+    }
+  }
+
+  return DefaultABIInfo::classifyReturnType(RetTy);
+}
+
 // TODO: this implementation is now likely redundant with
 // DefaultABIInfo::EmitVAArg.
 Address PPC32_SVR4_ABIInfo::EmitVAArg(CodeGenFunction &CGF, Address VAList,
@@ -4382,6 +4427,25 @@ Address PPC32_SVR4_ABIInfo::EmitVAArg(CodeGenFunction &CGF, Address VAList,
   return Result;
 }
 
+bool PPC32TargetCodeGenInfo::isStructReturnInRegABI(
+    const llvm::Triple &Triple, const CodeGenOptions &Opts) {
+  assert(Triple.getArch() == llvm::Triple::ppc);
+
+  switch (Opts.getStructReturnConvention()) {
+  case CodeGenOptions::SRCK_Default:
+    break;
+  case CodeGenOptions::SRCK_OnStack: // -maix-struct-return
+    return false;
+  case CodeGenOptions::SRCK_InRegs: // -msvr4-struct-return
+    return true;
+  }
+
+  if (Triple.isOSBinFormatELF() && !Triple.isOSLinux())
+    return true;
+
+  return false;
+}
+
 bool
 PPC32TargetCodeGenInfo::initDwarfEHRegSizeTable(CodeGen::CodeGenFunction &CGF,
                                                 llvm::Value *Address) const {
@@ -10264,10 +10328,14 @@ const TargetCodeGenInfo &CodeGenModule::getTargetCodeGenInfo() {
     return SetCGInfo(new ARMTargetCodeGenInfo(Types, Kind));
   }
 
-  case llvm::Triple::ppc:
+  case llvm::Triple::ppc: {
+    bool IsSoftFloat =
+        CodeGenOpts.FloatABI == "soft" || getTarget().hasFeature("spe");
+    bool RetSmallStructInRegABI =
+        PPC32TargetCodeGenInfo::isStructReturnInRegABI(Triple, CodeGenOpts);
     return SetCGInfo(
-        new PPC32TargetCodeGenInfo(Types, CodeGenOpts.FloatABI == "soft" ||
-                                   getTarget().hasFeature("spe")));
+        new PPC32TargetCodeGenInfo(Types, IsSoftFloat, RetSmallStructInRegABI));
+  }
   case llvm::Triple::ppc64:
     if (Triple.isOSBinFormatELF()) {
       PPC64_SVR4_ABIInfo::ABIKind Kind = PPC64_SVR4_ABIInfo::ELFv1;
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -4535,6 +4535,19 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back(A->getValue());
   }
 
+  if (Arg *A = Args.getLastArg(options::OPT_maix_struct_return,
+                               options::OPT_msvr4_struct_return)) {
+    if (TC.getArch() != llvm::Triple::ppc) {
+      D.Diag(diag::err_drv_unsupported_opt_for_target)
+          << A->getSpelling() << RawTriple.str();
+    } else if (A->getOption().matches(options::OPT_maix_struct_return)) {
+      CmdArgs.push_back("-maix-struct-return");
+    } else {
+      assert(A->getOption().matches(options::OPT_msvr4_struct_return));
+      CmdArgs.push_back("-msvr4-struct-return");
+    }
+  }
+
   if (Arg *A = Args.getLastArg(options::OPT_fpcc_struct_return,
                                options::OPT_freg_struct_return)) {
     if (TC.getArch() != llvm::Triple::x86) {
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1297,11 +1297,18 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
       Diags.Report(diag::err_drv_invalid_value) << A->getAsString(Args) << Val;
   }
 
-  if (Arg *A = Args.getLastArg(OPT_fpcc_struct_return, OPT_freg_struct_return)) {
-    if (A->getOption().matches(OPT_fpcc_struct_return)) {
+  // X86_32 has -fppc-struct-return and -freg-struct-return.
+  // PPC32 has -maix-struct-return and -msvr4-struct-return.
+  if (Arg *A =
+          Args.getLastArg(OPT_fpcc_struct_return, OPT_freg_struct_return,
+                          OPT_maix_struct_return, OPT_msvr4_struct_return)) {
+    const Option &O = A->getOption();
+    if (O.matches(OPT_fpcc_struct_return) ||
+        O.matches(OPT_maix_struct_return)) {
       Opts.setStructReturnConvention(CodeGenOptions::SRCK_OnStack);
     } else {
-      assert(A->getOption().matches(OPT_freg_struct_return));
+      assert(O.matches(OPT_freg_struct_return) ||
+             O.matches(OPT_msvr4_struct_return));
       Opts.setStructReturnConvention(CodeGenOptions::SRCK_InRegs);
     }
   }
diff --git a/clang/test/CodeGen/ppc32-struct-return.c b/clang/test/CodeGen/ppc32-struct-return.c
@@ -0,0 +1,88 @@
+// REQUIRES: powerpc-registered-target
+// RUN: %clang_cc1 -triple powerpc-unknown-freebsd \
+// RUN:   -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-SVR4
+// RUN: %clang_cc1 -triple powerpc-unknown-linux \
+// RUN:   -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-AIX
+// RUN: %clang_cc1 -triple powerpc-unknown-linux -maix-struct-return \
+// RUN:   -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-AIX
+// RUN: %clang_cc1 -triple powerpc-unknown-linux -msvr4-struct-return \
+// RUN:   -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-SVR4
+// RUN: %clang_cc1 -triple powerpc-unknown-netbsd \
+// RUN:   -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-SVR4
+// RUN: %clang_cc1 -triple powerpc-unknown-openbsd \
+// RUN:   -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-SVR4
+// RUN: %clang_cc1 -triple powerpc-unknown-openbsd -maix-struct-return \
+// RUN:   -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-AIX
+// RUN: %clang_cc1 -triple powerpc-unknown-openbsd -msvr4-struct-return \
+// RUN:   -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-SVR4
+
+typedef struct {
+} Zero;
+typedef struct {
+  char c;
+} One;
+typedef struct {
+  short s;
+} Two;
+typedef struct {
+  char c[3];
+} Three;
+typedef struct {
+  float f;
+} Four; // svr4 to return i32, not float
+typedef struct {
+  char c[5];
+} Five;
+typedef struct {
+  short s[3];
+} Six;
+typedef struct {
+  char c[7];
+} Seven;
+typedef struct {
+  int i;
+  char c;
+} Eight; // padded for alignment
+typedef struct {
+  char c[9];
+} Nine;
+
+// CHECK-AIX-LABEL: define void @ret0(%struct.Zero* noalias sret {{[^,]*}})
+// CHECK-SVR4-LABEL: define void @ret0()
+Zero ret0(void) { return (Zero){}; }
+
+// CHECK-AIX-LABEL: define void @ret1(%struct.One* noalias sret {{[^,]*}})
+// CHECK-SVR4-LABEL: define i8 @ret1()
+One ret1(void) { return (One){'a'}; }
+
+// CHECK-AIX-LABEL: define void @ret2(%struct.Two* noalias sret {{[^,]*}})
+// CHECK-SVR4-LABEL: define i16 @ret2()
+Two ret2(void) { return (Two){123}; }
+
+// CHECK-AIX-LABEL: define void @ret3(%struct.Three* noalias sret {{[^,]*}})
+// CHECK-SVR4-LABEL: define i24 @ret3()
+Three ret3(void) { return (Three){"abc"}; }
+
+// CHECK-AIX-LABEL: define void @ret4(%struct.Four* noalias sret {{[^,]*}})
+// CHECK-SVR4-LABEL: define i32 @ret4()
+Four ret4(void) { return (Four){0.4}; }
+
+// CHECK-AIX-LABEL: define void @ret5(%struct.Five* noalias sret {{[^,]*}})
+// CHECK-SVR4-LABEL: define i40 @ret5()
+Five ret5(void) { return (Five){"abcde"}; }
+
+// CHECK-AIX-LABEL: define void @ret6(%struct.Six* noalias sret {{[^,]*}})
+// CHECK-SVR4-LABEL: define i48 @ret6()
+Six ret6(void) { return (Six){12, 34, 56}; }
+
+// CHECK-AIX-LABEL: define void @ret7(%struct.Seven* noalias sret {{[^,]*}})
+// CHECK-SVR4-LABEL: define i56 @ret7()
+Seven ret7(void) { return (Seven){"abcdefg"}; }
+
+// CHECK-AIX-LABEL: define void @ret8(%struct.Eight* noalias sret {{[^,]*}})
+// CHECK-SVR4-LABEL: define i64 @ret8()
+Eight ret8(void) { return (Eight){123, 'a'}; }
+
+// CHECK-AIX-LABEL: define void @ret9(%struct.Nine* noalias sret {{[^,]*}})
+// CHECK-SVR4-LABEL: define void @ret9(%struct.Nine* noalias sret {{[^,]*}})
+Nine ret9(void) { return (Nine){"abcdefghi"}; }
diff --git a/clang/test/Driver/ppc-unsupported.c b/clang/test/Driver/ppc-unsupported.c
@@ -0,0 +1,10 @@
+// REQUIRES: powerpc-registered-target
+// RUN: not %clang -target powerpc64-unknown-freebsd -maix-struct-return \
+// RUN:   -c %s 2>&1 | FileCheck %s
+// RUN: not %clang -target powerpc64-unknown-freebsd -msvr4-struct-return \
+// RUN:   -c %s 2>&1 | FileCheck %s
+// RUN: not %clang -target powerpc64le-unknown-linux -maix-struct-return \
+// RUN:   -c %s 2>&1 | FileCheck %s
+// RUN: not %clang -target powerpc64le-unknown-linux -msvr4-struct-return \
+// RUN:   -c %s 2>&1 | FileCheck %s
+// CHECK: unsupported option
