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Function pointers under PPC64 ELFv1 (which is used on PPC64/Linux on the POWER7, A2 and earlier cores) are really pointers to a function descriptor, a structure with three pointers: the actual pointer to the code to which to jump, the pointer to the TOC needed by the callee, and an environment pointer. We used to chain these loads, and make them opaque to the rest of the optimizer, so that they'd always occur directly before the call. This is not necessary, and in fact, highly suboptimal on embedded cores. Once the function pointer is known, the loads can be performed ahead of time; in fact, they can be hoisted out of loops. Now these function descriptors are almost always generated by the linker, and thus the contents of the descriptors are invariant. As a result, by default, we'll mark the associated loads as invariant (allowing them to be hoisted out of loops). I've added a target feature to turn this off, however, just in case someone needs that option (constructing an on-stack descriptor, casting it to a function pointer, and then calling it cannot be well-defined C/C++ code, but I can imagine some JIT-compilation system doing so). Consider this simple test: $ cat call.c typedef void (*fp)(); void bar(fp x) { for (int i = 0; i < 1600000000; ++i) x(); } $ cat main.c typedef void (*fp)(); void bar(fp x); void foo() {} int main() { bar(foo); } On the PPC A2 (the BG/Q supercomputer), marking the function-descriptor loads as invariant brings the execution time down to ~8 seconds from ~32 seconds with the loads in the loop. The difference on the POWER7 is smaller. Compiling with: gcc -std=c99 -O3 -mcpu=native call.c main.c : ~6 seconds [this is 4.8.2] clang -O3 -mcpu=native call.c main.c : ~5.3 seconds clang -O3 -mcpu=native call.c main.c -mno-invariant-function-descriptors : ~4 seconds (looks like we'd benefit from additional loop unrolling here, as a first guess, because this is faster with the extra loads) The -mno-invariant-function-descriptors will be added to Clang shortly. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226207 91177308-0d34-0410-b5e6-96231b3b80d8
255 lines
8.4 KiB
C++
255 lines
8.4 KiB
C++
//===-- PPCTargetMachine.cpp - Define TargetMachine for PowerPC -----------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Top-level implementation for the PowerPC target.
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//
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//===----------------------------------------------------------------------===//
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#include "PPCTargetMachine.h"
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#include "PPC.h"
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#include "PPCTargetObjectFile.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/IR/Function.h"
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#include "llvm/MC/MCStreamer.h"
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#include "llvm/PassManager.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/FormattedStream.h"
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#include "llvm/Support/TargetRegistry.h"
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#include "llvm/Target/TargetOptions.h"
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#include "llvm/Transforms/Scalar.h"
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using namespace llvm;
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static cl::
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opt<bool> DisableCTRLoops("disable-ppc-ctrloops", cl::Hidden,
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cl::desc("Disable CTR loops for PPC"));
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static cl::opt<bool>
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VSXFMAMutateEarly("schedule-ppc-vsx-fma-mutation-early",
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cl::Hidden, cl::desc("Schedule VSX FMA instruction mutation early"));
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static cl::opt<bool>
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EnableGEPOpt("ppc-gep-opt", cl::Hidden,
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cl::desc("Enable optimizations on complex GEPs"),
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cl::init(true));
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extern "C" void LLVMInitializePowerPCTarget() {
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// Register the targets
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RegisterTargetMachine<PPC32TargetMachine> A(ThePPC32Target);
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RegisterTargetMachine<PPC64TargetMachine> B(ThePPC64Target);
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RegisterTargetMachine<PPC64TargetMachine> C(ThePPC64LETarget);
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}
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static std::string computeFSAdditions(StringRef FS, CodeGenOpt::Level OL, StringRef TT) {
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std::string FullFS = FS;
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Triple TargetTriple(TT);
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// Make sure 64-bit features are available when CPUname is generic
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if (TargetTriple.getArch() == Triple::ppc64 ||
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TargetTriple.getArch() == Triple::ppc64le) {
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if (!FullFS.empty())
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FullFS = "+64bit," + FullFS;
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else
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FullFS = "+64bit";
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}
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if (OL >= CodeGenOpt::Default) {
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if (!FullFS.empty())
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FullFS = "+crbits," + FullFS;
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else
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FullFS = "+crbits";
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}
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if (OL != CodeGenOpt::None) {
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if (!FullFS.empty())
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FullFS = "+invariant-function-descriptors," + FullFS;
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else
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FullFS = "+invariant-function-descriptors";
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}
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return FullFS;
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}
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static std::unique_ptr<TargetLoweringObjectFile> createTLOF(const Triple &TT) {
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// If it isn't a Mach-O file then it's going to be a linux ELF
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// object file.
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if (TT.isOSDarwin())
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return make_unique<TargetLoweringObjectFileMachO>();
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return make_unique<PPC64LinuxTargetObjectFile>();
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}
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// The FeatureString here is a little subtle. We are modifying the feature string
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// with what are (currently) non-function specific overrides as it goes into the
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// LLVMTargetMachine constructor and then using the stored value in the
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// Subtarget constructor below it.
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PPCTargetMachine::PPCTargetMachine(const Target &T, StringRef TT, StringRef CPU,
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StringRef FS, const TargetOptions &Options,
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Reloc::Model RM, CodeModel::Model CM,
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CodeGenOpt::Level OL)
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: LLVMTargetMachine(T, TT, CPU, computeFSAdditions(FS, OL, TT), Options, RM,
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CM, OL),
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TLOF(createTLOF(Triple(getTargetTriple()))),
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Subtarget(TT, CPU, TargetFS, *this) {
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initAsmInfo();
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}
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PPCTargetMachine::~PPCTargetMachine() {}
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void PPC32TargetMachine::anchor() { }
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PPC32TargetMachine::PPC32TargetMachine(const Target &T, StringRef TT,
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StringRef CPU, StringRef FS,
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const TargetOptions &Options,
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Reloc::Model RM, CodeModel::Model CM,
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CodeGenOpt::Level OL)
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: PPCTargetMachine(T, TT, CPU, FS, Options, RM, CM, OL) {
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}
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void PPC64TargetMachine::anchor() { }
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PPC64TargetMachine::PPC64TargetMachine(const Target &T, StringRef TT,
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StringRef CPU, StringRef FS,
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const TargetOptions &Options,
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Reloc::Model RM, CodeModel::Model CM,
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CodeGenOpt::Level OL)
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: PPCTargetMachine(T, TT, CPU, FS, Options, RM, CM, OL) {
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}
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const PPCSubtarget *
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PPCTargetMachine::getSubtargetImpl(const Function &F) const {
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AttributeSet FnAttrs = F.getAttributes();
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Attribute CPUAttr =
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FnAttrs.getAttribute(AttributeSet::FunctionIndex, "target-cpu");
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Attribute FSAttr =
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FnAttrs.getAttribute(AttributeSet::FunctionIndex, "target-features");
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std::string CPU = !CPUAttr.hasAttribute(Attribute::None)
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? CPUAttr.getValueAsString().str()
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: TargetCPU;
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std::string FS = !FSAttr.hasAttribute(Attribute::None)
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? FSAttr.getValueAsString().str()
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: TargetFS;
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auto &I = SubtargetMap[CPU + FS];
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if (!I) {
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// This needs to be done before we create a new subtarget since any
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// creation will depend on the TM and the code generation flags on the
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// function that reside in TargetOptions.
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resetTargetOptions(F);
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I = llvm::make_unique<PPCSubtarget>(TargetTriple, CPU, FS, *this);
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}
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return I.get();
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}
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//===----------------------------------------------------------------------===//
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// Pass Pipeline Configuration
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//===----------------------------------------------------------------------===//
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namespace {
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/// PPC Code Generator Pass Configuration Options.
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class PPCPassConfig : public TargetPassConfig {
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public:
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PPCPassConfig(PPCTargetMachine *TM, PassManagerBase &PM)
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: TargetPassConfig(TM, PM) {}
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PPCTargetMachine &getPPCTargetMachine() const {
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return getTM<PPCTargetMachine>();
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}
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const PPCSubtarget &getPPCSubtarget() const {
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return *getPPCTargetMachine().getSubtargetImpl();
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}
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void addIRPasses() override;
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bool addPreISel() override;
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bool addILPOpts() override;
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bool addInstSelector() override;
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void addPreRegAlloc() override;
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void addPreSched2() override;
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void addPreEmitPass() override;
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};
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} // namespace
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TargetPassConfig *PPCTargetMachine::createPassConfig(PassManagerBase &PM) {
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return new PPCPassConfig(this, PM);
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}
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void PPCPassConfig::addIRPasses() {
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addPass(createAtomicExpandPass(&getPPCTargetMachine()));
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if (TM->getOptLevel() == CodeGenOpt::Aggressive && EnableGEPOpt) {
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// Call SeparateConstOffsetFromGEP pass to extract constants within indices
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// and lower a GEP with multiple indices to either arithmetic operations or
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// multiple GEPs with single index.
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addPass(createSeparateConstOffsetFromGEPPass(TM, true));
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// Call EarlyCSE pass to find and remove subexpressions in the lowered
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// result.
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addPass(createEarlyCSEPass());
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// Do loop invariant code motion in case part of the lowered result is
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// invariant.
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addPass(createLICMPass());
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}
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TargetPassConfig::addIRPasses();
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}
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bool PPCPassConfig::addPreISel() {
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if (!DisableCTRLoops && getOptLevel() != CodeGenOpt::None)
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addPass(createPPCCTRLoops(getPPCTargetMachine()));
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return false;
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}
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bool PPCPassConfig::addILPOpts() {
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addPass(&EarlyIfConverterID);
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return true;
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}
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bool PPCPassConfig::addInstSelector() {
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// Install an instruction selector.
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addPass(createPPCISelDag(getPPCTargetMachine()));
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#ifndef NDEBUG
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if (!DisableCTRLoops && getOptLevel() != CodeGenOpt::None)
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addPass(createPPCCTRLoopsVerify());
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#endif
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addPass(createPPCVSXCopyPass());
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return false;
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}
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void PPCPassConfig::addPreRegAlloc() {
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initializePPCVSXFMAMutatePass(*PassRegistry::getPassRegistry());
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insertPass(VSXFMAMutateEarly ? &RegisterCoalescerID : &MachineSchedulerID,
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&PPCVSXFMAMutateID);
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}
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void PPCPassConfig::addPreSched2() {
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addPass(createPPCVSXCopyCleanupPass(), false);
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if (getOptLevel() != CodeGenOpt::None)
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addPass(&IfConverterID);
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}
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void PPCPassConfig::addPreEmitPass() {
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if (getOptLevel() != CodeGenOpt::None)
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addPass(createPPCEarlyReturnPass(), false);
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// Must run branch selection immediately preceding the asm printer.
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addPass(createPPCBranchSelectionPass(), false);
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}
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void PPCTargetMachine::addAnalysisPasses(PassManagerBase &PM) {
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// Add first the target-independent BasicTTI pass, then our PPC pass. This
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// allows the PPC pass to delegate to the target independent layer when
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// appropriate.
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PM.add(createBasicTargetTransformInfoPass(this));
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PM.add(createPPCTargetTransformInfoPass(this));
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}
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