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https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@5620 91177308-0d34-0410-b5e6-96231b3b80d8
110 lines
3.8 KiB
C++
110 lines
3.8 KiB
C++
//===-- Local.cpp - Functions to perform local transformations ------------===//
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//
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// This family of functions perform various local transformations to the
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// program.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/iTerminators.h"
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#include "llvm/ConstantHandling.h"
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//===----------------------------------------------------------------------===//
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// Local constant propogation...
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//
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// ConstantFoldInstruction - If an instruction references constants, try to fold
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// them together...
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//
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bool doConstantPropogation(BasicBlock::iterator &II) {
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if (Constant *C = ConstantFoldInstruction(II)) {
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// Replaces all of the uses of a variable with uses of the constant.
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II->replaceAllUsesWith(C);
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// Remove the instruction from the basic block...
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II = II->getParent()->getInstList().erase(II);
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return true;
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}
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return false;
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}
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// ConstantFoldTerminator - If a terminator instruction is predicated on a
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// constant value, convert it into an unconditional branch to the constant
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// destination.
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//
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bool ConstantFoldTerminator(BasicBlock *BB) {
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TerminatorInst *T = BB->getTerminator();
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// Branch - See if we are conditional jumping on constant
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if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
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if (BI->isUnconditional()) return false; // Can't optimize uncond branch
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BasicBlock *Dest1 = cast<BasicBlock>(BI->getOperand(0));
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BasicBlock *Dest2 = cast<BasicBlock>(BI->getOperand(1));
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if (ConstantBool *Cond = dyn_cast<ConstantBool>(BI->getCondition())) {
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// Are we branching on constant?
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// YES. Change to unconditional branch...
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BasicBlock *Destination = Cond->getValue() ? Dest1 : Dest2;
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BasicBlock *OldDest = Cond->getValue() ? Dest2 : Dest1;
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//cerr << "Function: " << T->getParent()->getParent()
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// << "\nRemoving branch from " << T->getParent()
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// << "\n\nTo: " << OldDest << endl;
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// Let the basic block know that we are letting go of it. Based on this,
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// it will adjust it's PHI nodes.
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assert(BI->getParent() && "Terminator not inserted in block!");
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OldDest->removePredecessor(BI->getParent());
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// Set the unconditional destination, and change the insn to be an
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// unconditional branch.
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BI->setUnconditionalDest(Destination);
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return true;
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}
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#if 0
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// FIXME: TODO: This doesn't work if the destination has PHI nodes with
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// different incoming values on each branch!
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//
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else if (Dest2 == Dest1) { // Conditional branch to same location?
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// This branch matches something like this:
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// br bool %cond, label %Dest, label %Dest
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// and changes it into: br label %Dest
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// Let the basic block know that we are letting go of one copy of it.
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assert(BI->getParent() && "Terminator not inserted in block!");
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Dest1->removePredecessor(BI->getParent());
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// Change a conditional branch to unconditional.
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BI->setUnconditionalDest(Dest1);
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return true;
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}
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#endif
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}
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return false;
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}
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//===----------------------------------------------------------------------===//
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// Local dead code elimination...
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//
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bool isInstructionTriviallyDead(Instruction *I) {
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return I->use_empty() && !I->mayWriteToMemory() && !isa<TerminatorInst>(I);
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}
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// dceInstruction - Inspect the instruction at *BBI and figure out if it's
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// [trivially] dead. If so, remove the instruction and update the iterator
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// to point to the instruction that immediately succeeded the original
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// instruction.
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//
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bool dceInstruction(BasicBlock::iterator &BBI) {
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// Look for un"used" definitions...
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if (isInstructionTriviallyDead(BBI)) {
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BBI = BBI->getParent()->getInstList().erase(BBI); // Bye bye
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return true;
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}
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return false;
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}
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