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This pass is now obsolete since all targets have moved to the SelectionDAG
infrastructure and the simple isels have been removed. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@24090 91177308-0d34-0410-b5e6-96231b3b80d8
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//===-- lib/Transforms/Scalar/LowerConstantExprs.cpp ------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was written by Vladimir Prus and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the LowerConstantExpression pass, which converts all
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// constant expressions into instructions. This is primarily usefull for
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// code generators which don't yet want or don't have a need to handle
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// constant expressions themself.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Pass.h"
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#include "llvm/Function.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/Support/InstIterator.h"
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#include <vector>
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#include <iostream>
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using namespace llvm;
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using namespace std;
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namespace {
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class ConstantExpressionsLower : public FunctionPass {
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private: // FunctionPass overrides
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bool runOnFunction(Function& f);
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private: // internal methods
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/// For all operands of 'insn' which are constant expressions, generates
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/// an appropriate instruction and replaces the use of constant
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/// expression with the use of the generated instruction.
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bool runOnInstruction(Instruction& insn);
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/// Given an constant expression 'c' which occures in 'instruction',
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/// at position 'pos',
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/// generates instruction to compute 'c' and replaces the use of 'c'
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/// with the use of that instruction. This handles only top-level
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/// expression in 'c', any subexpressions are not handled.
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Instruction* convert(const ConstantExpr& c, Instruction* where);
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};
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RegisterOpt<ConstantExpressionsLower> X(
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"lowerconstantexprs", "Lower constant expressions");
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}
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bool ConstantExpressionsLower::runOnFunction(Function& f)
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{
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bool modified = false;
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for (inst_iterator i = inst_begin(f), e = inst_end(f); i != e; ++i)
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{
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modified |= runOnInstruction(*i);
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}
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return modified;
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}
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bool ConstantExpressionsLower::runOnInstruction(Instruction& instruction)
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{
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bool modified = false;
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for (unsigned pos = 0; pos < instruction.getNumOperands(); ++pos)
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{
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if (ConstantExpr* ce
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= dyn_cast<ConstantExpr>(instruction.getOperand(pos))) {
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// Decide where to insert the new instruction
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Instruction* where = &instruction;
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// For PHI nodes we can't insert new instruction before phi,
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// since phi should always come at the beginning of the
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// basic block.
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// So, we need to insert it in the predecessor, right before
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// the terminating instruction.
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if (PHINode* p = dyn_cast<PHINode>(&instruction)) {
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BasicBlock* predecessor = 0;
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for(unsigned i = 0; i < p->getNumIncomingValues(); ++i)
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if (p->getIncomingValue(i) == ce) {
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predecessor = p->getIncomingBlock(i);
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break;
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}
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assert(predecessor && "could not find predecessor");
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where = predecessor->getTerminator();
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}
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Instruction* n = convert(*ce, where);
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// Note: we can't call replaceAllUsesWith, since
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// that might replace uses in another functions,
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// where the instruction(s) we've generated are not
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// available.
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// Moreover, we can't replace all the users in the same
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// function, because we can't be sure the definition
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// made in this block will be available in other
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// places where the constant is used.
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instruction.setOperand(pos, n);
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// The new instruction might have constant expressions in
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// it. Extract them too.
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runOnInstruction(*n);
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modified = true;
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}
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}
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return modified;
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}
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Instruction*
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ConstantExpressionsLower::convert(const ConstantExpr& c, Instruction* where)
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{
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Instruction* result = 0;
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if (c.getOpcode() >= Instruction::BinaryOpsBegin &&
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c.getOpcode() < Instruction::BinaryOpsEnd)
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{
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result = BinaryOperator::create(
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static_cast<Instruction::BinaryOps>(c.getOpcode()),
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c.getOperand(0), c.getOperand(1), "", where);
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}
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else
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{
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switch(c.getOpcode()) {
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case Instruction::GetElementPtr:
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{
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vector<Value*> idx;
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for (unsigned i = 1; i < c.getNumOperands(); ++i)
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idx.push_back(c.getOperand(i));
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result = new GetElementPtrInst(c.getOperand(0),
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idx, "", where);
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break;
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}
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case Instruction::Cast:
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result = new CastInst(c.getOperand(0), c.getType(), "",
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where);
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break;
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case Instruction::Shl:
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case Instruction::Shr:
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result = new ShiftInst(
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static_cast<Instruction::OtherOps>(c.getOpcode()),
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c.getOperand(0), c.getOperand(1), "", where);
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break;
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case Instruction::Select:
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result = new SelectInst(c.getOperand(0), c.getOperand(1),
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c.getOperand(2), "", where);
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break;
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default:
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std::cerr << "Offending expr: " << c << "\n";
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assert(0 && "Constant expression not yet handled!\n");
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}
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}
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return result;
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}
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namespace llvm {
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FunctionPass* createLowerConstantExpressionsPass()
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{
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return new ConstantExpressionsLower;
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}
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}
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