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//===- ReplaceConstant.cpp - Replace LLVM constant expression--------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements a utility function for replacing LLVM constant
// expressions by instructions.
//
//===----------------------------------------------------------------------===//
#include "llvm/IR/ReplaceConstant.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/ValueMap.h"
namespace llvm {
void convertConstantExprsToInstructions(Instruction *I, ConstantExpr *CE,
SmallPtrSetImpl<Instruction *> *Insts) {
// Collect all reachable paths to CE from constant exprssion operands of I.
std::map<Use *, std::vector<std::vector<ConstantExpr *>>> CEPaths;
collectConstantExprPaths(I, CE, CEPaths);
// Convert all constant expressions to instructions which are collected at
// CEPaths.
convertConstantExprsToInstructions(I, CEPaths, Insts);
}
void convertConstantExprsToInstructions(
Instruction *I,
std::map<Use *, std::vector<std::vector<ConstantExpr *>>> &CEPaths,
SmallPtrSetImpl<Instruction *> *Insts) {
ValueMap<ConstantExpr *, Instruction *> Visited;
for (Use &U : I->operands()) {
// The operand U is either not a constant expression operand or the
// constant expression paths do not belong to U, ignore U.
if (!CEPaths.count(&U))
continue;
// If the instruction I is a PHI instruction, then fix the instruction
// insertion point to the entry of the incoming basic block for operand U.
auto *BI = I;
if (auto *Phi = dyn_cast<PHINode>(I)) {
BasicBlock *BB = Phi->getIncomingBlock(U);
BI = &(*(BB->getFirstInsertionPt()));
}
// Go through all the paths associated with operand U, and convert all the
// constant expressions along all the paths to corresponding instructions.
auto *II = I;
auto &Paths = CEPaths[&U];
for (auto &Path : Paths) {
for (auto *CE : Path) {
// Instruction which is equivalent to CE.
Instruction *NI = nullptr;
if (!Visited.count(CE)) {
// CE is encountered first time, convert it into a corresponding
// instruction NI, and appropriately insert NI before the parent
// instruction.
NI = CE->getAsInstruction(BI);
// Mark CE as visited by mapping CE to NI.
Visited[CE] = NI;
// If required collect NI.
if (Insts)
Insts->insert(NI);
} else {
// We had already encountered CE, the correponding instruction already
// exist, use it to replace CE.
NI = Visited[CE];
}
assert(NI && "Expected an instruction corresponding to constant "
"expression.");
// Replace all uses of constant expression CE by the corresponding
// instruction NI within the current parent instruction.
II->replaceUsesOfWith(CE, NI);
BI = II = NI;
}
}
}
// Remove all converted constant expressions which are dead by now.
for (auto Item : Visited)
Item.first->removeDeadConstantUsers();
}
void collectConstantExprPaths(
Instruction *I, ConstantExpr *CE,
std::map<Use *, std::vector<std::vector<ConstantExpr *>>> &CEPaths) {
for (Use &U : I->operands()) {
// If the operand U is not a constant expression operand, then ignore it.
auto *CE2 = dyn_cast<ConstantExpr>(U.get());
if (!CE2)
continue;
// Holds all reachable paths from CE2 to CE.
std::vector<std::vector<ConstantExpr *>> Paths;
// Collect all reachable paths from CE2 to CE.
std::vector<ConstantExpr *> Path{CE2};
std::vector<std::vector<ConstantExpr *>> Stack{Path};
while (!Stack.empty()) {
std::vector<ConstantExpr *> TPath = Stack.back();
Stack.pop_back();
auto *CE3 = TPath.back();
if (CE3 == CE) {
Paths.push_back(TPath);
continue;
}
for (auto &UU : CE3->operands()) {
if (auto *CE4 = dyn_cast<ConstantExpr>(UU.get())) {
std::vector<ConstantExpr *> NPath(TPath.begin(), TPath.end());
NPath.push_back(CE4);
Stack.push_back(NPath);
}
}
}
// Associate all the collected paths with U, and save it.
if (!Paths.empty())
CEPaths[&U] = Paths;
}
}
} // namespace llvm
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