[tblgen] GCC/MS builtin to target intrisics map.

[speziale.ettore]

Summary

Allow TableGen to generate static functions to perform GCC/MS builtin name to
target specific intrinsic ID mapping.

[speziale.ettore]

This patch would allows backend to make use of the builtin-to-intrinsic mapping function if requested. In the case no builtin names are associated with intrinsics, the builtin-to-instrinsic table is not emitted to avoid warnings about zero-length arrays.

[rnk]

lgtm

Can you give an example of what this would enable?

[speziale.ettore]

In D31150#705628, @rnk wrote:

lgtm

Can you give an example of what this would enable?

The use case is a module which contains function calls a particular backend would like to lower into intrinsic calls. Enabling the builtin-to-intrinsics map would allow to automate a little bit that process.

[rnk]

In D31150#705657, @speziale.ettore wrote:

In D31150#705628, @rnk wrote:

lgtm

Can you give an example of what this would enable?

The use case is a module which contains function calls a particular backend would like to lower into intrinsic calls. Enabling the builtin-to-intrinsics map would allow to automate a little bit that process.

I mean an example target-specific builtin that you need to map.

[speziale.ettore]

I mean an example target-specific builtin that you need to map.

Sorry, I misunderstood your question.

My use case is related to languages where there are a lot of functions which can be lowered into intrinsics calls by backends. For instance in OpenCL there are a set of functions that allow to query the property of the NDRange. For instance the size_t get_global_size(uint x) function allows to get the number of work items along the x dimension:

size_t foo() {
  return get_global_size(1);
}

This is the code generated by clang:

define i64 @foo() local_unnamed_addr #0 {
entry:
  %call = tail call i64 @get_global_size(i32 1) #2
  ret i64 %call
}

Backend for architectures supporting this kind of languages often exposes intrinsics to access those informations, hence I would like to use the builtin-to-intrinsic map to rewrite the call to get_global_size to the call to a target-specify intrinsic before starting the final code generation.

In my case, the backend I'm working on is not upstream, so I cannot give you an example only using upstream code.

[speziale.ettore]

Gently ping.

[speziale.ettore]

Quentin/Reid could you please commit this one if there are no objections? (I do not have commits rights).

[speziale.ettore]

Closing, as Aditya already committed this -- see trunk@r300735.

include/llvm/TableGen/StringToOffsetTable.h

   std::string AggregateString;
 
 public:
+  bool Empty() const { return StringOffset.empty(); }
+
   unsigned GetOrAddStringOffset(StringRef Str, bool appendZero = true) {
     auto IterBool =
         StringOffset.insert(std::make_pair(Str, AggregateString.size()));

utils/TableGen/IntrinsicEmitter.cpp

   // Emit the intrinsic parameter attributes.
   EmitAttributes(Ints, OS);
 
-  // Individual targets don't need GCC builtin name mappings.
-  if (!TargetOnly) {
-    // Emit code to translate GCC builtins into LLVM intrinsics.
-    EmitIntrinsicToBuiltinMap(Ints, true, OS);
+  // Emit code to translate GCC builtins into LLVM intrinsics.
+  EmitIntrinsicToBuiltinMap(Ints, true, OS);
 
-    // Emit code to translate MS builtins into LLVM intrinsics.
-    EmitIntrinsicToBuiltinMap(Ints, false, OS);
-  }
 
   EmitSuffix(OS);
 }

        << "Builtin(const char "
        << "*TargetPrefixStr, StringRef BuiltinNameStr) {\n";
   }
+
+  if (Table.Empty()) {
+    OS << "  return ";
+    if (!TargetPrefix.empty())
+      OS << "(" << TargetPrefix << "Intrinsic::ID)";
+    OS << "Intrinsic::not_intrinsic;\n";
+    OS << "}\n";
+    OS << "#endif\n\n";
+    return;
+  }
+
   OS << "  static const char BuiltinNames[] = {\n";
   Table.EmitCharArray(OS);
   OS << "  };\n\n";