[mips] Support `micromips` attribute

[atanasyan]

Summary

This patch adds support for the micromips and nomicromips attributes for MIPS targets.

[sdardis]

include/clang/Basic/AttrDocs.td

1277–1278

instructs the backend to locally select or turn off microMIPS code generation.

I think we can improve this to:

"instructs the backend to generate or not to generate microMIPS code for that function."

lib/Sema/SemaDeclAttr.cpp

5945

This is incorrect. microMIPS can be used to support interrupt handlers as the instruction set supports returning from an exception with 'eret'. MIPS16e lacks the 'eret' instruction, so it cannot be used with an interrupt handler function.

Aside: it is implementation dependant which ISAmode is used when an interrupt occurs on a processor supporting microMIPS and MIPS32R3 from my reading of the specification.

[atanasyan]

Thanks for review.

This changes:

• Allow simultaneous using of micromips and interrupt attributes.
• Fix wording of micromips attribute description.

[sdardis]

LGTM.

include/clang/Basic/Attr.td

let Args = [EnumArgument<"Interrupt", "InterruptType",
                             "vector=hw4", "vector=hw5", "eic", ""],
                            ["sw0", "sw1", "hw0", "hw1", "hw2", "hw3",
                             "hw4", "hw5", "eic", "eic"]
                            >];
   let ParseKind = "Interrupt";
   let Documentation = [MipsInterruptDocs];
 }
 
+def MicroMips : InheritableAttr, TargetSpecificAttr<TargetMips> {
+  let Spellings = [GCC<"micromips">];
+  let Subjects = SubjectList<[Function], ErrorDiag>;
+  let Documentation = [MicroMipsDocs];
+}
+
 def Mode : Attr {
   let Spellings = [GCC<"mode">];
   let Subjects = SubjectList<[Var, Enum, TypedefName, Field], ErrorDiag,
                              "ExpectedVariableEnumFieldOrTypedef">;
   let Args = [IdentifierArgument<"Mode">];
   let Documentation = [Undocumented];
 }
 

 }
 
 def NoMips16 : InheritableAttr, TargetSpecificAttr<TargetMips> {
   let Spellings = [GCC<"nomips16">];
   let Subjects = SubjectList<[Function], ErrorDiag>;
   let Documentation = [Undocumented];
 }
 
+def NoMicroMips : InheritableAttr, TargetSpecificAttr<TargetMips> {
+  let Spellings = [GCC<"nomicromips">];
+  let Subjects = SubjectList<[Function], ErrorDiag>;
+  let Documentation = [MicroMipsDocs];
+}
+
 // This is not a TargetSpecificAttr so that is silently accepted and
 // ignored on other targets as encouraged by the OpenCL spec.
 //
 // See OpenCL 1.2 6.11.5: "It is our intention that a particular
 // implementation of OpenCL be free to ignore all attributes and the
 // resulting executable binary will produce the same result."
 //
 // However, only AMD GPU targets will emit the corresponding IR

include/clang/Basic/AttrDocs.td

 - The function return sequence is changed to use an exception return instruction.
 
 - The parameter sets the interrupt mask for the function corresponding to the
   interrupt level specified. If no mask is specified the interrupt mask
   defaults to "eic".
   }];
 }
 
+def MicroMipsDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+Clang supports the GNU style ``__attribute__((micromips))`` and
+``__attribute__((nomicromips))`` attributes on MIPS targets. These attributes
+may be attached to a function definition and instructs the backend to generate
+or not to generate microMIPS code for that function.
+
+These attributes override the -mmicromips and -mno-micromips options
+on the command line.
+  }];
+}
+
 def AVRInterruptDocs : Documentation {
   let Category = DocCatFunction;
   let Content = [{
 Clang supports the GNU style ``__attribute__((interrupt))`` attribute on
 AVR targets. This attribute may be attached to a function definition and instructs
 the backend to generate appropriate function entry/exit code so that it can be used
 directly as an interrupt service routine.
 

lib/CodeGen/TargetInfo.cpp

void setTargetAttributes(const Decl *D, llvm::GlobalValue *GV,
     llvm::Function *Fn = cast<llvm::Function>(GV);
     if (FD->hasAttr<Mips16Attr>()) {
       Fn->addFnAttr("mips16");
     }
     else if (FD->hasAttr<NoMips16Attr>()) {
       Fn->addFnAttr("nomips16");
     }
 
+    if (FD->hasAttr<MicroMipsAttr>())
+      Fn->addFnAttr("micromips");
+    else if (FD->hasAttr<NoMicroMipsAttr>())
+      Fn->addFnAttr("nomicromips");
+
     const MipsInterruptAttr *Attr = FD->getAttr<MipsInterruptAttr>();
     if (!Attr)
       return;
 
     const char *Kind;
     switch (Attr->getInterrupt()) {
     case MipsInterruptAttr::eic:     Kind = "eic"; break;
     case MipsInterruptAttr::sw0:     Kind = "sw0"; break;

lib/Sema/SemaDeclAttr.cpp

static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case AttributeList::AT_X86ForceAlignArgPointer:
     handleX86ForceAlignArgPointerAttr(S, D, Attr);
     break;
   case AttributeList::AT_DLLExport:
   case AttributeList::AT_DLLImport:
     handleDLLAttr(S, D, Attr);
     break;
   case AttributeList::AT_Mips16:
-    handleSimpleAttributeWithExclusions<Mips16Attr, MipsInterruptAttr>(S, D,
-                                                                       Attr);
+    handleSimpleAttributeWithExclusions<Mips16Attr, MicroMipsAttr,
+                                        MipsInterruptAttr>(S, D, Attr);
     break;
   case AttributeList::AT_NoMips16:
     handleSimpleAttribute<NoMips16Attr>(S, D, Attr);
     break;
+  case AttributeList::AT_MicroMips:
+    handleSimpleAttributeWithExclusions<MicroMipsAttr, Mips16Attr>(S, D, Attr);
+    break;
+  case AttributeList::AT_NoMicroMips:
+    handleSimpleAttribute<NoMicroMipsAttr>(S, D, Attr);
+    break;
   case AttributeList::AT_AMDGPUFlatWorkGroupSize:
     handleAMDGPUFlatWorkGroupSizeAttr(S, D, Attr);
     break;
   case AttributeList::AT_AMDGPUWavesPerEU:
     handleAMDGPUWavesPerEUAttr(S, D, Attr);
     break;
   case AttributeList::AT_AMDGPUNumSGPR:
     handleAMDGPUNumSGPRAttr(S, D, Attr);

test/CodeGen/micromips-attr.c

+// RUN: %clang_cc1 -triple mips-linux-gnu -emit-llvm  -o  - %s | FileCheck %s
+
+void __attribute__((micromips)) foo (void) {}
+
+// CHECK: define void @foo() [[MICROMIPS:#[0-9]+]]
+
+void __attribute__((nomicromips)) nofoo (void) {}
+
+// CHECK: define void @nofoo() [[NOMICROMIPS:#[0-9]+]]
+
+// CHECK: attributes [[MICROMIPS]] = { noinline nounwind {{.*}} "micromips" {{.*}} }
+// CHECK: attributes [[NOMICROMIPS]]  = { noinline nounwind {{.*}} "nomicromips" {{.*}} }

test/Misc/pragma-attribute-supported-attributes-list.test

 // RUN: clang-tblgen -gen-clang-test-pragma-attribute-supported-attributes -I%src_include_dir %src_include_dir/clang/Basic/Attr.td -o - | FileCheck %s
 
 // The number of supported attributes should never go down!
 
-// CHECK: #pragma clang attribute supports 60 attributes:
+// CHECK: #pragma clang attribute supports 62 attributes:
 // CHECK-NEXT: AMDGPUFlatWorkGroupSize (SubjectMatchRule_function)
 // CHECK-NEXT: AMDGPUNumSGPR (SubjectMatchRule_function)
 // CHECK-NEXT: AMDGPUNumVGPR (SubjectMatchRule_function)
 // CHECK-NEXT: AMDGPUWavesPerEU (SubjectMatchRule_function)
 // CHECK-NEXT: AVRSignal (SubjectMatchRule_function)
 // CHECK-NEXT: AbiTag (SubjectMatchRule_record_not_is_union, SubjectMatchRule_variable, SubjectMatchRule_function, SubjectMatchRule_namespace)
 // CHECK-NEXT: AlignValue (SubjectMatchRule_variable, SubjectMatchRule_type_alias)
 // CHECK-NEXT: AllocSize (SubjectMatchRule_function)

 // CHECK-NEXT: EnableIf (SubjectMatchRule_function)
 // CHECK-NEXT: EnumExtensibility (SubjectMatchRule_enum)
 // CHECK-NEXT: ExternalSourceSymbol ((SubjectMatchRule_record, SubjectMatchRule_enum, SubjectMatchRule_enum_constant, SubjectMatchRule_field, SubjectMatchRule_function, SubjectMatchRule_namespace, SubjectMatchRule_objc_category, SubjectMatchRule_objc_interface, SubjectMatchRule_objc_method, SubjectMatchRule_objc_property, SubjectMatchRule_objc_protocol, SubjectMatchRule_record, SubjectMatchRule_type_alias, SubjectMatchRule_variable))
 // CHECK-NEXT: FlagEnum (SubjectMatchRule_enum)
 // CHECK-NEXT: Flatten (SubjectMatchRule_function)
 // CHECK-NEXT: IFunc (SubjectMatchRule_function)
 // CHECK-NEXT: InternalLinkage (SubjectMatchRule_variable, SubjectMatchRule_function, SubjectMatchRule_record)
 // CHECK-NEXT: LTOVisibilityPublic (SubjectMatchRule_record)
+// CHECK-NEXT: MicroMips (SubjectMatchRule_function)
 // CHECK-NEXT: NoDebug (SubjectMatchRule_hasType_functionType, SubjectMatchRule_objc_method, SubjectMatchRule_variable_not_is_parameter)
 // CHECK-NEXT: NoDuplicate (SubjectMatchRule_function)
+// CHECK-NEXT: NoMicroMips (SubjectMatchRule_function)
 // CHECK-NEXT: NoSanitize (SubjectMatchRule_function, SubjectMatchRule_objc_method, SubjectMatchRule_variable_is_global)
 // CHECK-NEXT: NoSanitizeSpecific (SubjectMatchRule_function, SubjectMatchRule_variable_is_global)
 // CHECK-NEXT: NoSplitStack (SubjectMatchRule_function)
 // CHECK-NEXT: NotTailCalled (SubjectMatchRule_function)
 // CHECK-NEXT: ObjCBoxable (SubjectMatchRule_record)
 // CHECK-NEXT: ObjCMethodFamily (SubjectMatchRule_objc_method)
 // CHECK-NEXT: ObjCRequiresSuper (SubjectMatchRule_objc_method)
 // CHECK-NEXT: ObjCRuntimeName (SubjectMatchRule_objc_interface, SubjectMatchRule_objc_protocol)

test/Sema/attr-micromips.c

+// RUN: %clang_cc1 -triple mips-linux-gnu -fsyntax-only -verify %s
+
+__attribute__((nomicromips(0))) void foo1();  // expected-error {{'nomicromips' attribute takes no arguments}}
+__attribute__((micromips(1))) void foo2();    // expected-error {{'micromips' attribute takes no arguments}}
+
+__attribute((nomicromips)) int a; // expected-error {{attribute only applies to functions}}
+__attribute((micromips)) int b;   // expected-error {{attribute only applies to functions}}
+
+__attribute__((micromips,mips16)) void foo5();  // expected-error {{'micromips' and 'mips16' attributes are not compatible}} \
+                                                // expected-note {{conflicting attribute is here}}
+__attribute__((mips16,micromips)) void foo6();  // expected-error {{'mips16' and 'micromips' attributes are not compatible}} \
+                                                // expected-note {{conflicting attribute is here}}
+
+__attribute((micromips)) void foo7();
+__attribute((nomicromips)) void foo8();