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//==- RISCVPromoteConstant.cpp - Promote constant fp to global for RISC-V --==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "RISCV.h"
#include "RISCVSubtarget.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/TargetLowering.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
using namespace llvm;
#define DEBUG_TYPE "riscv-promote-const"
#define RISCV_PROMOTE_CONSTANT_NAME "RISC-V Promote Constants"
STATISTIC(NumPromoted, "Number of constant literals promoted to globals");
STATISTIC(NumPromotedUses, "Number of uses of promoted literal constants");
namespace {
class RISCVPromoteConstant : public ModulePass {
public:
static char ID;
RISCVPromoteConstant() : ModulePass(ID) {}
StringRef getPassName() const override { return RISCV_PROMOTE_CONSTANT_NAME; }
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<TargetPassConfig>();
AU.setPreservesCFG();
}
/// Iterate over the functions and promote the double fp constants that
/// would otherwise go into the constant pool to a constant array.
bool runOnModule(Module &M) override {
if (skipModule(M))
return false;
// TargetMachine and Subtarget are needed to query isFPImmlegal.
const TargetPassConfig &TPC = getAnalysis<TargetPassConfig>();
const TargetMachine &TM = TPC.getTM<TargetMachine>();
bool Changed = false;
for (Function &F : M) {
const RISCVSubtarget &ST = TM.getSubtarget<RISCVSubtarget>(F);
const RISCVTargetLowering *TLI = ST.getTargetLowering();
Changed |= runOnFunction(F, TLI);
}
return Changed;
}
private:
bool runOnFunction(Function &F, const RISCVTargetLowering *TLI);
};
} // end anonymous namespace
char RISCVPromoteConstant::ID = 0;
INITIALIZE_PASS(RISCVPromoteConstant, DEBUG_TYPE, RISCV_PROMOTE_CONSTANT_NAME,
false, false)
ModulePass *llvm::createRISCVPromoteConstantPass() {
return new RISCVPromoteConstant();
}
bool RISCVPromoteConstant::runOnFunction(Function &F,
const RISCVTargetLowering *TLI) {
if (F.hasOptNone() || F.hasOptSize())
return false;
// Bail out and make no transformation if the target doesn't support
// doubles, or if we're not targeting RV64 as we currently see some
// regressions for those targets.
if (!TLI->isTypeLegal(MVT::f64) || !TLI->isTypeLegal(MVT::i64))
return false;
// Collect all unique double constants and their uses in the function. Use
// MapVector to preserve insertion order.
MapVector<ConstantFP *, SmallVector<Use *, 8>> ConstUsesMap;
for (Instruction &I : instructions(F)) {
for (Use &U : I.operands()) {
auto *C = dyn_cast<ConstantFP>(U.get());
if (!C || !C->getType()->isDoubleTy())
continue;
// Do not promote if it wouldn't be loaded from the constant pool.
if (TLI->isFPImmLegal(C->getValueAPF(), MVT::f64,
/*ForCodeSize=*/false))
continue;
// Do not promote a constant if it is used as an immediate argument
// for an intrinsic.
if (auto *II = dyn_cast<IntrinsicInst>(U.getUser())) {
Function *IntrinsicFunc = II->getFunction();
unsigned OperandIdx = U.getOperandNo();
if (IntrinsicFunc && IntrinsicFunc->getAttributes().hasParamAttr(
OperandIdx, Attribute::ImmArg)) {
LLVM_DEBUG(dbgs() << "Skipping promotion of constant in: " << *II
<< " because operand " << OperandIdx
<< " must be an immediate.\n");
continue;
}
}
// Note: FP args to inline asm would be problematic if we had a
// constraint that required an immediate floating point operand. At the
// time of writing LLVM doesn't recognise such a constraint.
ConstUsesMap[C].push_back(&U);
}
}
int PromotableConstants = ConstUsesMap.size();
LLVM_DEBUG(dbgs() << "Found " << PromotableConstants
<< " promotable constants in " << F.getName() << "\n");
// Bail out if no promotable constants found, or if only one is found.
if (PromotableConstants < 2) {
LLVM_DEBUG(dbgs() << "Performing no promotions as insufficient promotable "
"constants found\n");
return false;
}
NumPromoted += PromotableConstants;
// Create a global array containing the promoted constants.
Module *M = F.getParent();
Type *DoubleTy = Type::getDoubleTy(M->getContext());
SmallVector<Constant *, 16> ConstantVector;
for (auto const &Pair : ConstUsesMap)
ConstantVector.push_back(Pair.first);
ArrayType *ArrayTy = ArrayType::get(DoubleTy, ConstantVector.size());
Constant *GlobalArrayInitializer =
ConstantArray::get(ArrayTy, ConstantVector);
auto *GlobalArray = new GlobalVariable(
*M, ArrayTy,
/*isConstant=*/true, GlobalValue::InternalLinkage, GlobalArrayInitializer,
".promoted_doubles." + F.getName());
// A cache to hold the loaded value for a given constant within a basic block.
DenseMap<std::pair<ConstantFP *, BasicBlock *>, Value *> LocalLoads;
// Replace all uses with the loaded value.
unsigned Idx = 0;
for (auto const &Pair : ConstUsesMap) {
ConstantFP *Const = Pair.first;
const SmallVector<Use *, 8> &Uses = Pair.second;
for (Use *U : Uses) {
Instruction *UserInst = cast<Instruction>(U->getUser());
BasicBlock *InsertionBB;
// If the user is a PHI node, we must insert the load in the
// corresponding predecessor basic block. Otherwise, it's inserted into
// the same block as the use.
if (auto *PN = dyn_cast<PHINode>(UserInst))
InsertionBB = PN->getIncomingBlock(*U);
else
InsertionBB = UserInst->getParent();
if (isa<CatchSwitchInst>(InsertionBB->getTerminator())) {
LLVM_DEBUG(dbgs() << "Bailing out: catchswitch means thre is no valid "
"insertion point.\n");
return false;
}
auto CacheKey = std::make_pair(Const, InsertionBB);
Value *LoadedVal = nullptr;
// Re-use a load if it exists in the insertion block.
if (LocalLoads.count(CacheKey)) {
LoadedVal = LocalLoads.at(CacheKey);
} else {
// Otherwise, create a new GEP and Load at the correct insertion point.
// It is always safe to insert in the first insertion point in the BB,
// so do that and let other passes reorder.
IRBuilder<> Builder(InsertionBB, InsertionBB->getFirstInsertionPt());
Value *ElementPtr = Builder.CreateConstInBoundsGEP2_64(
GlobalArray->getValueType(), GlobalArray, 0, Idx, "double.addr");
LoadedVal = Builder.CreateLoad(DoubleTy, ElementPtr, "double.val");
// Cache the newly created load for this block.
LocalLoads[CacheKey] = LoadedVal;
}
U->set(LoadedVal);
++NumPromotedUses;
}
++Idx;
}
return true;
}
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