Reintroduce the InlineHint function attribute.

This time it's for real! I am going to hook this up in the frontends as well.

The inliner has some experimental heuristics for dealing with the inline hint.
When given a -respect-inlinehint option, functions marked with the inline
keyword are given a threshold just above the default for -O3.

We need some experiments to determine if that is the right thing to do.

llvm-svn: 95466

bindings/ocaml/llvm/llvm.ml

@@ -93,6 +93,7 @@ module Attribute = struct
   | Noredzone
   | Noimplicitfloat
   | Naked
+  | Inlinehint
 end
 
 module Icmp = struct

bindings/ocaml/llvm/llvm.mli

@@ -143,6 +143,7 @@ module Attribute : sig
   | Noredzone
   | Noimplicitfloat
   | Naked
+  | Inlinehint
 end
 
 (** The predicate for an integer comparison ([icmp]) instruction.

docs/LangRef.html

@@ -1083,6 +1083,11 @@ define void @f() optsize { ... }
       function into callers whenever possible, ignoring any active inlining size
       threshold for this caller.</dd>
 
+  <dt><tt><b>inlinehint</b></tt></dt>
+  <dd>This attribute indicates that the source code contained a hint that inlining
+      this function is desirable (such as the "inline" keyword in C/C++).  It
+      is just a hint; it imposes no requirements on the inliner.</dd>
+
   <dt><tt><b>noinline</b></tt></dt>
   <dd>This attribute indicates that the inliner should never inline this
       function in any situation. This attribute may not be used together with

include/llvm-c/Core.h

@@ -118,7 +118,8 @@ typedef enum {
     LLVMNoCaptureAttribute  = 1<<21,
     LLVMNoRedZoneAttribute  = 1<<22,
     LLVMNoImplicitFloatAttribute = 1<<23,
-    LLVMNakedAttribute      = 1<<24
+    LLVMNakedAttribute      = 1<<24,
+    LLVMInlineHintAttribute = 1<<25
 } LLVMAttribute;
 
 typedef enum {

include/llvm/Attributes.h

@@ -58,6 +58,8 @@ const Attributes NoRedZone = 1<<22; /// disable redzone
 const Attributes NoImplicitFloat = 1<<23; /// disable implicit floating point
                                           /// instructions.
 const Attributes Naked           = 1<<24; ///< Naked function
+const Attributes InlineHint      = 1<<25; ///< source said inlining was
+                                          ///desirable
 
 /// @brief Attributes that only apply to function parameters.
 const Attributes ParameterOnly = ByVal | Nest | StructRet | NoCapture;
@@ -66,7 +68,7 @@ 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 | Naked;
+  NoRedZone | NoImplicitFloat | Naked | InlineHint;
 
 /// @brief Parameter attributes that do not apply to vararg call arguments.
 const Attributes VarArgsIncompatible = StructRet;

include/llvm/Transforms/IPO/InlinerPass.h

@@ -52,10 +52,11 @@ struct Inliner : public CallGraphSCCPass {
   unsigned getInlineThreshold() const { return InlineThreshold; }
 
   /// Calculate the inline threshold for given Caller. This threshold is lower
-  /// if Caller is marked with OptimizeForSize and -inline-threshold is not
-  /// given on the comand line.
+  /// if the caller is marked with OptimizeForSize and -inline-threshold is not
+  /// given on the comand line. It is higher if the callee is marked with the
+  /// inlinehint attribute.
   ///
-  unsigned getInlineThreshold(Function* Caller) const;
+  unsigned getInlineThreshold(CallSite CS) const;
 
   /// getInlineCost - This method must be implemented by the subclass to
   /// determine the cost of inlining the specified call site.  If the cost

lib/AsmParser/LLLexer.cpp

@@ -558,6 +558,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(readnone);
   KEYWORD(readonly);
 
+  KEYWORD(inlinehint);
   KEYWORD(noinline);
   KEYWORD(alwaysinline);
   KEYWORD(optsize);

lib/AsmParser/LLParser.cpp

@@ -947,6 +947,7 @@ bool LLParser::ParseOptionalAttrs(unsigned &Attrs, unsigned AttrKind) {
     case lltok::kw_noinline:        Attrs |= Attribute::NoInline; break;
     case lltok::kw_readnone:        Attrs |= Attribute::ReadNone; break;
     case lltok::kw_readonly:        Attrs |= Attribute::ReadOnly; break;
+    case lltok::kw_inlinehint:      Attrs |= Attribute::InlineHint; break;
     case lltok::kw_alwaysinline:    Attrs |= Attribute::AlwaysInline; break;
     case lltok::kw_optsize:         Attrs |= Attribute::OptimizeForSize; break;
     case lltok::kw_ssp:             Attrs |= Attribute::StackProtect; break;

lib/AsmParser/LLToken.h

@@ -85,6 +85,7 @@ namespace lltok {
     kw_readnone,
     kw_readonly,
 
+    kw_inlinehint,
     kw_noinline,
     kw_alwaysinline,
     kw_optsize,

lib/Target/CppBackend/CPPBackend.cpp

@@ -470,6 +470,7 @@ namespace {
         HANDLE_ATTR(Nest);
         HANDLE_ATTR(ReadNone);
         HANDLE_ATTR(ReadOnly);
+        HANDLE_ATTR(InlineHint);
         HANDLE_ATTR(NoInline);
         HANDLE_ATTR(AlwaysInline);
         HANDLE_ATTR(OptimizeForSize);

lib/Transforms/IPO/Inliner.cpp

@@ -41,6 +41,16 @@ static cl::opt<int>
 InlineLimit("inline-threshold", cl::Hidden, cl::init(225), cl::ZeroOrMore,
         cl::desc("Control the amount of inlining to perform (default = 225)"));
 
+static cl::opt<bool>
+RespectHint("respect-inlinehint", cl::Hidden,
+            cl::desc("Respect the inlinehint attribute"));
+
+// Threshold to use when inlinehint is given.
+const int HintThreshold = 300;
+
+// Threshold to use when optsize is specified (and there is no -inline-limit).
+const int OptSizeThreshold = 75;
+
 Inliner::Inliner(void *ID) 
   : CallGraphSCCPass(ID), InlineThreshold(InlineLimit) {}
 
@@ -172,13 +182,21 @@ static bool InlineCallIfPossible(CallSite CS, CallGraph &CG,
   return true;
 }
 
-unsigned Inliner::getInlineThreshold(Function* Caller) const {
+unsigned Inliner::getInlineThreshold(CallSite CS) const {
+  // Listen to inlinehint when -respect-inlinehint is given.
+  Function *Callee = CS.getCalledFunction();
+  if (RespectHint && Callee && !Callee->isDeclaration() &&
+      Callee->hasFnAttr(Attribute::InlineHint))
+    return HintThreshold;
+
+  // Listen to optsize when -inline-limit is not given.
+  Function *Caller = CS.getCaller();
   if (Caller && !Caller->isDeclaration() &&
       Caller->hasFnAttr(Attribute::OptimizeForSize) &&
       InlineLimit.getNumOccurrences() == 0)
-    return 75;
-  else
-    return InlineThreshold;
+      return OptSizeThreshold;
+
+  return InlineThreshold;
 }
 
 /// shouldInline - Return true if the inliner should attempt to inline
@@ -200,7 +218,7 @@ bool Inliner::shouldInline(CallSite CS) {
   
   int Cost = IC.getValue();
   Function *Caller = CS.getCaller();
-  int CurrentThreshold = getInlineThreshold(Caller);
+  int CurrentThreshold = getInlineThreshold(CS);
   float FudgeFactor = getInlineFudgeFactor(CS);
   if (Cost >= (int)(CurrentThreshold * FudgeFactor)) {
     DEBUG(dbgs() << "    NOT Inlining: cost=" << Cost
@@ -236,8 +254,7 @@ bool Inliner::shouldInline(CallSite CS) {
 
       outerCallsFound = true;
       int Cost2 = IC2.getValue();
-      Function *Caller2 = CS2.getCaller();
-      int CurrentThreshold2 = getInlineThreshold(Caller2);
+      int CurrentThreshold2 = getInlineThreshold(CS2);
       float FudgeFactor2 = getInlineFudgeFactor(CS2);
 
       if (Cost2 >= (int)(CurrentThreshold2 * FudgeFactor2))

lib/VMCore/Attributes.cpp

@@ -56,6 +56,8 @@ std::string Attribute::getAsString(Attributes Attrs) {
     Result += "optsize ";
   if (Attrs & Attribute::NoInline)
     Result += "noinline ";
+  if (Attrs & Attribute::InlineHint)
+    Result += "inlinehint ";
   if (Attrs & Attribute::AlwaysInline)
     Result += "alwaysinline ";
   if (Attrs & Attribute::StackProtect)

utils/llvm.grm

@@ -161,6 +161,7 @@ FuncAttr      ::= noreturn
  | signext
  | readnone
  | readonly
+ | inlinehint
  | noinline
  | alwaysinline
  | optsize

utils/vim/llvm.vim

@@ -51,7 +51,7 @@ syn keyword llvmKeyword volatile fastcc coldcc cc ccc
 syn keyword llvmKeyword x86_stdcallcc x86_fastcallcc
 syn keyword llvmKeyword signext zeroext inreg sret nounwind noreturn
 syn keyword llvmKeyword nocapture byval nest readnone readonly noalias
-syn keyword llvmKeyword noinline alwaysinline optsize ssp sspreq
+syn keyword llvmKeyword inlinehint noinline alwaysinline optsize ssp sspreq
 syn keyword llvmKeyword noredzone noimplicitfloat naked
 syn keyword llvmKeyword module asm align tail to
 syn keyword llvmKeyword addrspace section alias sideeffect c gc