mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2025-11-04 05:17:07 +00:00
fd93908ae8
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21427 91177308-0d34-0410-b5e6-96231b3b80d8
92 lines
3.8 KiB
C++
92 lines
3.8 KiB
C++
//===- DemoteRegToStack.cpp - Move a virtual register to the stack --------===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file was developed by the LLVM research group and is distributed under
|
|
// the University of Illinois Open Source License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file provide the function DemoteRegToStack(). This function takes a
|
|
// virtual register computed by an Instruction and replaces it with a slot in
|
|
// the stack frame, allocated via alloca. It returns the pointer to the
|
|
// AllocaInst inserted. After this function is called on an instruction, we are
|
|
// guaranteed that the only user of the instruction is a store that is
|
|
// immediately after it.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/Transforms/Utils/Local.h"
|
|
#include "llvm/Function.h"
|
|
#include "llvm/Instructions.h"
|
|
#include "llvm/Type.h"
|
|
#include <map>
|
|
using namespace llvm;
|
|
|
|
/// DemoteRegToStack - This function takes a virtual register computed by an
|
|
/// Instruction and replaces it with a slot in the stack frame, allocated via
|
|
/// alloca. This allows the CFG to be changed around without fear of
|
|
/// invalidating the SSA information for the value. It returns the pointer to
|
|
/// the alloca inserted to create a stack slot for I.
|
|
///
|
|
AllocaInst* llvm::DemoteRegToStack(Instruction &I) {
|
|
if (I.use_empty()) return 0; // nothing to do!
|
|
|
|
// Create a stack slot to hold the value.
|
|
Function *F = I.getParent()->getParent();
|
|
AllocaInst *Slot = new AllocaInst(I.getType(), 0, I.getName(),
|
|
F->getEntryBlock().begin());
|
|
|
|
// Change all of the users of the instruction to read from the stack slot
|
|
// instead.
|
|
while (!I.use_empty()) {
|
|
Instruction *U = cast<Instruction>(I.use_back());
|
|
if (PHINode *PN = dyn_cast<PHINode>(U)) {
|
|
// If this is a PHI node, we can't insert a load of the value before the
|
|
// use. Instead, insert the load in the predecessor block corresponding
|
|
// to the incoming value.
|
|
//
|
|
// Note that if there are multiple edges from a basic block to this PHI
|
|
// node that we cannot multiple loads. The problem is that the resultant
|
|
// PHI node will have multiple values (from each load) coming in from the
|
|
// same block, which is illegal SSA form. For this reason, we keep track
|
|
// and reuse loads we insert.
|
|
std::map<BasicBlock*, Value*> Loads;
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
|
|
if (PN->getIncomingValue(i) == &I) {
|
|
Value *&V = Loads[PN->getIncomingBlock(i)];
|
|
if (V == 0) {
|
|
// Insert the load into the predecessor block
|
|
V = new LoadInst(Slot, I.getName()+".reload",
|
|
PN->getIncomingBlock(i)->getTerminator());
|
|
}
|
|
PN->setIncomingValue(i, V);
|
|
}
|
|
|
|
} else {
|
|
// If this is a normal instruction, just insert a load.
|
|
Value *V = new LoadInst(Slot, I.getName()+".reload", U);
|
|
U->replaceUsesOfWith(&I, V);
|
|
}
|
|
}
|
|
|
|
|
|
// Insert stores of the computed value into the stack slot. We have to be
|
|
// careful is I is an invoke instruction though, because we can't insert the
|
|
// store AFTER the terminator instruction.
|
|
if (!isa<TerminatorInst>(I)) {
|
|
BasicBlock::iterator InsertPt = &I;
|
|
for (++InsertPt; isa<PHINode>(InsertPt); ++InsertPt)
|
|
/* empty */; // Don't insert before any PHI nodes.
|
|
new StoreInst(&I, Slot, InsertPt);
|
|
} else {
|
|
// FIXME: We cannot yet demote invoke instructions to the stack, because
|
|
// doing so would require breaking critical edges. This should be fixed
|
|
// eventually.
|
|
assert(0 &&
|
|
"Cannot demote the value computed by an invoke instruction yet!");
|
|
}
|
|
|
|
return Slot;
|
|
}
|