llvm-cpufeatures.cpp
// This file is a part of Julia. License is MIT: https://julialang.org/license
// Lower intrinsics that expose subtarget information to the language. This makes it
// possible to write code that changes behavior based on, e.g., the availability of
// specific CPU features.
//
// The following intrinsics are supported:
// - julia.cpu.have_fma.$typ: returns 1 if the platform supports hardware-accelerated FMA.
//
// Some of these intrinsics are overloaded, i.e., they are suffixed with a type name.
// To extend support, make sure codegen (in intrinsics.cpp) knows how to emit them.
//
// XXX: can / do we want to make this a codegen pass to enable querying TargetPassConfig
// instead of using the global target machine?
#include "llvm-version.h"
#include <llvm/IR/Module.h>
#include <llvm/IR/Constants.h>
#include <llvm/IR/Instructions.h>
#include <llvm/IR/PassManager.h>
#include <llvm/IR/LegacyPassManager.h>
#include <llvm/Target/TargetMachine.h>
#include <llvm/Support/Debug.h>
#include "julia.h"
#define DEBUG_TYPE "cpufeatures"
using namespace llvm;
extern TargetMachine *jl_TargetMachine;
// whether this platform unconditionally (i.e. without needing multiversioning) supports FMA
Optional<bool> always_have_fma(Function &intr) {
auto intr_name = intr.getName();
auto typ = intr_name.substr(strlen("julia.cpu.have_fma."));
#if defined(_CPU_AARCH64_)
return typ == "f32" || typ == "f64";
#else
(void)typ;
return {};
#endif
}
bool have_fma(Function &intr, Function &caller) {
auto unconditional = always_have_fma(intr);
if (unconditional.hasValue())
return unconditional.getValue();
auto intr_name = intr.getName();
auto typ = intr_name.substr(strlen("julia.cpu.have_fma."));
Attribute FSAttr = caller.getFnAttribute("target-features");
StringRef FS =
FSAttr.isValid() ? FSAttr.getValueAsString() : jl_TargetMachine->getTargetFeatureString();
SmallVector<StringRef, 6> Features;
FS.split(Features, ',');
for (StringRef Feature : Features)
#if defined _CPU_ARM_
if (Feature == "+vfp4")
return typ == "f32" || typ == "f64";
else if (Feature == "+vfp4sp")
return typ == "f32";
#else
if (Feature == "+fma" || Feature == "+fma4")
return typ == "f32" || typ == "f64";
#endif
return false;
}
void lowerHaveFMA(Function &intr, Function &caller, CallInst *I) {
if (have_fma(intr, caller))
I->replaceAllUsesWith(ConstantInt::get(I->getType(), 1));
else
I->replaceAllUsesWith(ConstantInt::get(I->getType(), 0));
return;
}
bool lowerCPUFeatures(Module &M)
{
SmallVector<Instruction*,6> Materialized;
for (auto &F: M.functions()) {
auto FN = F.getName();
if (FN.startswith("julia.cpu.have_fma.")) {
for (Use &U: F.uses()) {
User *RU = U.getUser();
CallInst *I = cast<CallInst>(RU);
lowerHaveFMA(F, *I->getParent()->getParent(), I);
Materialized.push_back(I);
}
}
}
if (!Materialized.empty()) {
for (auto I: Materialized) {
I->eraseFromParent();
}
return true;
} else {
return false;
}
}
struct CPUFeatures : PassInfoMixin<CPUFeatures> {
PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
};
PreservedAnalyses CPUFeatures::run(Module &M, ModuleAnalysisManager &AM)
{
lowerCPUFeatures(M);
return PreservedAnalyses::all();
}
namespace {
struct CPUFeaturesLegacy : public ModulePass {
static char ID;
CPUFeaturesLegacy() : ModulePass(ID) {};
bool runOnModule(Module &M)
{
return lowerCPUFeatures(M);
}
};
char CPUFeaturesLegacy::ID = 0;
static RegisterPass<CPUFeaturesLegacy>
Y("CPUFeatures",
"Lower calls to CPU feature testing intrinsics.",
false,
false);
}
Pass *createCPUFeaturesPass()
{
return new CPUFeaturesLegacy();
}
extern "C" JL_DLLEXPORT void LLVMExtraAddCPUFeaturesPass_impl(LLVMPassManagerRef PM)
{
unwrap(PM)->add(createCPUFeaturesPass());
}