Add support for naked functions

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76198 91177308-0d34-0410-b5e6-96231b3b80d8

docs/LangRef.html

@@ -1109,6 +1109,9 @@ red zone, even if the target-specific ABI normally permits it.
 <dt><tt>noimplicitfloat</tt></dt>
 <dd>This attributes disables implicit floating point instructions.</dd>
 
+<dt><tt>naked</tt></dt>
+<dd>This attribute disables prologue / epilogue emission for the function</dd>
+
 </dl>
 
 </div>

include/llvm-c/Core.h

@@ -98,7 +98,8 @@ typedef enum {
     LLVMByValAttribute      = 1<<7,
     LLVMNestAttribute       = 1<<8,
     LLVMReadNoneAttribute   = 1<<9,
-    LLVMReadOnlyAttribute   = 1<<10
+    LLVMReadOnlyAttribute   = 1<<10,
+    LLVMNakedAttribute      = 1<<24
 } LLVMAttribute;
 
 typedef enum {

include/llvm/Attributes.h

@@ -57,6 +57,7 @@ const Attributes NoCapture = 1<<21; ///< Function creates no aliases of pointer
 const Attributes NoRedZone = 1<<22; /// disable redzone
 const Attributes NoImplicitFloat = 1<<23; /// disable implicit floating point
                                           /// instructions.
+const Attributes Naked     = 1<<24; ///< Naked function
 
 /// @brief Attributes that only apply to function parameters.
 const Attributes ParameterOnly = ByVal | Nest | StructRet | NoCapture;
@@ -65,7 +66,7 @@ const Attributes ParameterOnly = ByVal | Nest | StructRet | NoCapture;
 /// be used on return values or function parameters.
 const Attributes FunctionOnly = NoReturn | NoUnwind | ReadNone | ReadOnly | 
   NoInline | AlwaysInline | OptimizeForSize | StackProtect | StackProtectReq |
-  NoRedZone | NoImplicitFloat;
+  NoRedZone | NoImplicitFloat | Naked;
 
 /// @brief Parameter attributes that do not apply to vararg call arguments.
 const Attributes VarArgsIncompatible = StructRet;

lib/AsmParser/LLLexer.cpp

@@ -541,6 +541,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(sspreq);
   KEYWORD(noredzone);
   KEYWORD(noimplicitfloat);
+  KEYWORD(naked);
 
   KEYWORD(type);
   KEYWORD(opaque);

lib/AsmParser/LLParser.cpp

@@ -775,6 +775,7 @@ bool LLParser::ParseOptionalAttrs(unsigned &Attrs, unsigned AttrKind) {
     case lltok::kw_sspreq:          Attrs |= Attribute::StackProtectReq; break;
     case lltok::kw_noredzone:       Attrs |= Attribute::NoRedZone; break;
     case lltok::kw_noimplicitfloat: Attrs |= Attribute::NoImplicitFloat; break;
+    case lltok::kw_naked:           Attrs |= Attribute::Naked; break;
         
     case lltok::kw_align: {
       unsigned Alignment;

lib/AsmParser/LLToken.h

@@ -84,6 +84,7 @@ namespace lltok {
     kw_sspreq,
     kw_noredzone,
     kw_noimplicitfloat,
+    kw_naked,
 
     kw_type,
     kw_opaque,

lib/CodeGen/PrologEpilogInserter.cpp

@@ -51,6 +51,7 @@ FunctionPass *llvm::createPrologEpilogCodeInserter() { return new PEI(); }
 /// frame indexes with appropriate references.
 ///
 bool PEI::runOnMachineFunction(MachineFunction &Fn) {
+  const Function* F = Fn.getFunction();
   const TargetRegisterInfo *TRI = Fn.getTarget().getRegisterInfo();
   RS = TRI->requiresRegisterScavenging(Fn) ? new RegScavenger() : NULL;
 
@@ -80,6 +81,7 @@ bool PEI::runOnMachineFunction(MachineFunction &Fn) {
   placeCSRSpillsAndRestores(Fn);
 
   // Add the code to save and restore the callee saved registers
+  if (!F->hasFnAttr(Attribute::Naked))
     insertCSRSpillsAndRestores(Fn);
 
   // Allow the target machine to make final modifications to the function
@@ -94,6 +96,7 @@ bool PEI::runOnMachineFunction(MachineFunction &Fn) {
   // called functions.  Because of this, calculateCalleeSavedRegisters
   // must be called before this function in order to set the HasCalls
   // and MaxCallFrameSize variables.
+  if (!F->hasFnAttr(Attribute::Naked))
     insertPrologEpilogCode(Fn);
 
   // Replace all MO_FrameIndex operands with physical register references

lib/VMCore/Attributes.cpp

@@ -63,6 +63,8 @@ std::string Attribute::getAsString(Attributes Attrs) {
     Result += "noredzone ";
   if (Attrs & Attribute::NoImplicitFloat)
     Result += "noimplicitfloat ";
+  if (Attrs & Attribute::Naked)
+    Result += "naked ";
   if (Attrs & Attribute::Alignment) {
     Result += "align ";
     Result += utostr(Attribute::getAlignmentFromAttrs(Attrs));