[TableGen][PGO] Disable profile instrumentation for printInstruction function

[xur]

Summary

We are seeing extremely long time in building AMDGPUInstPrinter.cpp when profile instrumentation is enabled: It takes more than 5 minutes (compared to ~ 8 seconds in non-instrument build)

This caused by the huge statements in printInsruction functions. In profile instrumentation build, we need have extra
control flow to differentiate each case statement. This in turn adds significant compile time in block placement and branch folding.

Function printInstruction is not likely to benefit from PGO build as it's rarely executed in a typical compilation.
So here I disable the profile instrumentation for this function.

[davidxl]

Does it have the same issue with FE instrumentation? The only thing to consider here is the coverage test may be affected.

[xur]

In D111682#3060328, @davidxl wrote:

Does it have the same issue with FE instrumentation? The only thing to consider here is the coverage test may be affected.

Yes. This would disable FE instrumentation also. I think FE instrumentation has the same long compile time issue.

[rnk]

Conceptually, it seems fine. As is, this will break the MSVC build, right? It doesn't support __attribute__. You need to add a portability macro in Compiler.h, or use ifdefs inline.

[xur]

Reid: thanks for pointing out the error for MSC. I move the Macro definition to compiler.h.

[rnk]

llvm/include/llvm/Support/Compiler.h

561

Is the && defined(__GNUC__) necessary? There are two ways to get clang to not define __GNUC__: target MSVC (clang-cl) or pass -fgnuc-version=0. In both cases, we would probably want to disable PGO instrumentation for printInstruction. I think __has_attribute is sufficient.

[xur]

llvm/include/llvm/Support/Compiler.h

561

I add "&& defined(GNUC) to exclude MSVC target, because I thought has_attribute(no_profile_instrument_function) return true for MSVC also.
In that case, I need to use GNUC. (As like you noticed, attribute__ is not available in MSVC)

Are you saying __has_attribute(no_profile_instrument_function) return false for MSVC?

I don't know the macro to disable instrumentation in MSVC? I cannot find in MSVC documents.

[rnk]

llvm/include/llvm/Support/Compiler.h

38

__has_attribute is defined to false here if it is not available. I believe that will handle MSVC.

[xur]

llvm/include/llvm/Support/Compiler.h

38

Is this for has_attriubte itself? I thought __has_attribute(<attribute>) is defined in some config.

For example, the "noinline" attribute, it is also defined for MSVC -- otherwise, the check of MSC_VER is useless.

#if has_attribute(noinline)
#define LLVM_ATTRIBUTE_NOINLINE attribute((noinline))
#elif defined(_MSC_VER)
#define LLVM_ATTRIBUTE_NOINLINE declspec(noinline)
#else
#define LLVM_ATTRIBUTE_NOINLINE
#endif

[xur]

llvm/include/llvm/Support/Compiler.h

38

I take back the last message. I read the code wrong.

[xur]

Integrated Reid's review comment.

[rnk]

lgtm, thanks!

llvm/include/llvm/Support/Compiler.h

 # define __has_feature(x) 0
 #endif
 
 #ifndef __has_extension
 # define __has_extension(x) 0
 #endif
 
 #ifndef __has_attribute
 # define __has_attribute(x) 0
 #endif
 
 #ifndef __has_builtin
 # define __has_builtin(x) 0
 #endif
 
 // Only use __has_cpp_attribute in C++ mode. GCC defines __has_cpp_attribute in
 // C mode, but the :: in __has_cpp_attribute(scoped::attribute) is invalid.

 #if __has_feature(cxx_exceptions)
 #define LLVM_ENABLE_EXCEPTIONS 1
 #elif defined(__GNUC__) && defined(__EXCEPTIONS)
 #define LLVM_ENABLE_EXCEPTIONS 1
 #elif defined(_MSC_VER) && defined(_CPPUNWIND)
 #define LLVM_ENABLE_EXCEPTIONS 1
 #endif
 
+/// \macro LLVM_NO_PROFILE_INSTRUMENT_FUNCTION
+/// Disable the profile instrument for a function.
+#if __has_attribute(no_profile_instrument_function)
+#define LLVM_NO_PROFILE_INSTRUMENT_FUNCTION                                    \
+  __attribute__((no_profile_instrument_function))
+#else
+#define LLVM_NO_PROFILE_INSTRUMENT_FUNCTION
+#endif
+
 #endif

llvm/utils/TableGen/AsmWriterEmitter.cpp

void AsmWriterEmitter::EmitPrintInstruction(
     raw_ostream &O,
     std::vector<std::vector<std::string>> &TableDrivenOperandPrinters,
     unsigned &BitsLeft, unsigned &AsmStrBits) {
   const unsigned OpcodeInfoBits = 64;
   Record *AsmWriter = Target.getAsmWriter();
   StringRef ClassName = AsmWriter->getValueAsString("AsmWriterClassName");
   bool PassSubtarget = AsmWriter->getValueAsInt("PassSubtarget");
 
+  // This function has some huge switch statements that causing excessive
+  // compile time in LLVM profile instrumenation build. This print function
+  // usually is not frequently called in compilation. Here we disable the
+  // profile instrumenation for this function.
   O << "/// printInstruction - This method is automatically generated by "
        "tablegen\n"
        "/// from the instruction set description.\n"
+       "LLVM_NO_PROFILE_INSTRUMENT_FUNCTION\n"
        "void "
     << Target.getName() << ClassName
     << "::printInstruction(const MCInst *MI, uint64_t Address, "
     << (PassSubtarget ? "const MCSubtargetInfo &STI, " : "")
     << "raw_ostream &O) {\n";
 
   // Emit the initial tab character.
   O << "  O << \"\\t\";\n\n";