mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-12-22 23:31:32 +00:00
72dba254ae
to find loops if the From and To instructions were in the same block. Refactor the code a little now that we need to fill to start the CFG-walking algorithm with more than one starting basic block sometimes. Special thanks to Andrew Trick for catching an error in my understanding of natural loops in code review. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188236 91177308-0d34-0410-b5e6-96231b3b80d8
245 lines
8.7 KiB
C++
245 lines
8.7 KiB
C++
//===-- CFG.cpp - BasicBlock analysis --------------------------------------==//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This family of functions performs analyses on basic blocks, and instructions
|
|
// contained within basic blocks.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/Analysis/CFG.h"
|
|
|
|
#include "llvm/ADT/SmallSet.h"
|
|
#include "llvm/Analysis/Dominators.h"
|
|
#include "llvm/Analysis/LoopInfo.h"
|
|
|
|
using namespace llvm;
|
|
|
|
/// FindFunctionBackedges - Analyze the specified function to find all of the
|
|
/// loop backedges in the function and return them. This is a relatively cheap
|
|
/// (compared to computing dominators and loop info) analysis.
|
|
///
|
|
/// The output is added to Result, as pairs of <from,to> edge info.
|
|
void llvm::FindFunctionBackedges(const Function &F,
|
|
SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) {
|
|
const BasicBlock *BB = &F.getEntryBlock();
|
|
if (succ_begin(BB) == succ_end(BB))
|
|
return;
|
|
|
|
SmallPtrSet<const BasicBlock*, 8> Visited;
|
|
SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack;
|
|
SmallPtrSet<const BasicBlock*, 8> InStack;
|
|
|
|
Visited.insert(BB);
|
|
VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
|
|
InStack.insert(BB);
|
|
do {
|
|
std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back();
|
|
const BasicBlock *ParentBB = Top.first;
|
|
succ_const_iterator &I = Top.second;
|
|
|
|
bool FoundNew = false;
|
|
while (I != succ_end(ParentBB)) {
|
|
BB = *I++;
|
|
if (Visited.insert(BB)) {
|
|
FoundNew = true;
|
|
break;
|
|
}
|
|
// Successor is in VisitStack, it's a back edge.
|
|
if (InStack.count(BB))
|
|
Result.push_back(std::make_pair(ParentBB, BB));
|
|
}
|
|
|
|
if (FoundNew) {
|
|
// Go down one level if there is a unvisited successor.
|
|
InStack.insert(BB);
|
|
VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
|
|
} else {
|
|
// Go up one level.
|
|
InStack.erase(VisitStack.pop_back_val().first);
|
|
}
|
|
} while (!VisitStack.empty());
|
|
}
|
|
|
|
/// GetSuccessorNumber - Search for the specified successor of basic block BB
|
|
/// and return its position in the terminator instruction's list of
|
|
/// successors. It is an error to call this with a block that is not a
|
|
/// successor.
|
|
unsigned llvm::GetSuccessorNumber(BasicBlock *BB, BasicBlock *Succ) {
|
|
TerminatorInst *Term = BB->getTerminator();
|
|
#ifndef NDEBUG
|
|
unsigned e = Term->getNumSuccessors();
|
|
#endif
|
|
for (unsigned i = 0; ; ++i) {
|
|
assert(i != e && "Didn't find edge?");
|
|
if (Term->getSuccessor(i) == Succ)
|
|
return i;
|
|
}
|
|
}
|
|
|
|
/// isCriticalEdge - Return true if the specified edge is a critical edge.
|
|
/// Critical edges are edges from a block with multiple successors to a block
|
|
/// with multiple predecessors.
|
|
bool llvm::isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum,
|
|
bool AllowIdenticalEdges) {
|
|
assert(SuccNum < TI->getNumSuccessors() && "Illegal edge specification!");
|
|
if (TI->getNumSuccessors() == 1) return false;
|
|
|
|
const BasicBlock *Dest = TI->getSuccessor(SuccNum);
|
|
const_pred_iterator I = pred_begin(Dest), E = pred_end(Dest);
|
|
|
|
// If there is more than one predecessor, this is a critical edge...
|
|
assert(I != E && "No preds, but we have an edge to the block?");
|
|
const BasicBlock *FirstPred = *I;
|
|
++I; // Skip one edge due to the incoming arc from TI.
|
|
if (!AllowIdenticalEdges)
|
|
return I != E;
|
|
|
|
// If AllowIdenticalEdges is true, then we allow this edge to be considered
|
|
// non-critical iff all preds come from TI's block.
|
|
while (I != E) {
|
|
const BasicBlock *P = *I;
|
|
if (P != FirstPred)
|
|
return true;
|
|
// Note: leave this as is until no one ever compiles with either gcc 4.0.1
|
|
// or Xcode 2. This seems to work around the pred_iterator assert in PR 2207
|
|
E = pred_end(P);
|
|
++I;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
// LoopInfo contains a mapping from basic block to the innermost loop. Find
|
|
// the outermost loop in the loop nest that contains BB.
|
|
static const Loop *getOutermostLoop(LoopInfo *LI, const BasicBlock *BB) {
|
|
const Loop *L = LI->getLoopFor(BB);
|
|
if (L) {
|
|
while (const Loop *Parent = L->getParentLoop())
|
|
L = Parent;
|
|
}
|
|
return L;
|
|
}
|
|
|
|
// True if there is a loop which contains both BB1 and BB2.
|
|
static bool loopContainsBoth(LoopInfo *LI,
|
|
const BasicBlock *BB1, const BasicBlock *BB2) {
|
|
const Loop *L1 = getOutermostLoop(LI, BB1);
|
|
const Loop *L2 = getOutermostLoop(LI, BB2);
|
|
return L1 != NULL && L1 == L2;
|
|
}
|
|
|
|
static bool isPotentiallyReachableInner(SmallVectorImpl<BasicBlock *> &Worklist,
|
|
BasicBlock *StopBB,
|
|
DominatorTree *DT, LoopInfo *LI) {
|
|
// When the stop block is unreachable, it's dominated from everywhere,
|
|
// regardless of whether there's a path between the two blocks.
|
|
if (DT && !DT->isReachableFromEntry(StopBB))
|
|
DT = 0;
|
|
|
|
// Limit the number of blocks we visit. The goal is to avoid run-away compile
|
|
// times on large CFGs without hampering sensible code. Arbitrarily chosen.
|
|
unsigned Limit = 32;
|
|
SmallSet<const BasicBlock*, 64> Visited;
|
|
do {
|
|
BasicBlock *BB = Worklist.pop_back_val();
|
|
if (!Visited.insert(BB))
|
|
continue;
|
|
if (BB == StopBB)
|
|
return true;
|
|
if (DT && DT->dominates(BB, StopBB))
|
|
return true;
|
|
if (LI && loopContainsBoth(LI, BB, StopBB))
|
|
return true;
|
|
|
|
if (!--Limit) {
|
|
// We haven't been able to prove it one way or the other. Conservatively
|
|
// answer true -- that there is potentially a path.
|
|
return true;
|
|
}
|
|
|
|
if (const Loop *Outer = LI ? getOutermostLoop(LI, BB) : 0) {
|
|
// All blocks in a single loop are reachable from all other blocks. From
|
|
// any of these blocks, we can skip directly to the exits of the loop,
|
|
// ignoring any other blocks inside the loop body.
|
|
Outer->getExitBlocks(Worklist);
|
|
} else {
|
|
for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
|
|
Worklist.push_back(*I);
|
|
}
|
|
} while (!Worklist.empty());
|
|
|
|
// We have exhausted all possible paths and are certain that 'To' can not be
|
|
// reached from 'From'.
|
|
return false;
|
|
}
|
|
|
|
bool llvm::isPotentiallyReachable(const BasicBlock *A, const BasicBlock *B,
|
|
DominatorTree *DT, LoopInfo *LI) {
|
|
assert(A->getParent() == B->getParent() &&
|
|
"This analysis is function-local!");
|
|
|
|
SmallVector<BasicBlock*, 32> Worklist;
|
|
Worklist.push_back(const_cast<BasicBlock*>(A));
|
|
|
|
return isPotentiallyReachableInner(Worklist, const_cast<BasicBlock*>(B),
|
|
DT, LI);
|
|
}
|
|
|
|
bool llvm::isPotentiallyReachable(const Instruction *A, const Instruction *B,
|
|
DominatorTree *DT, LoopInfo *LI) {
|
|
assert(A->getParent()->getParent() == B->getParent()->getParent() &&
|
|
"This analysis is function-local!");
|
|
|
|
SmallVector<BasicBlock*, 32> Worklist;
|
|
|
|
if (A->getParent() == B->getParent()) {
|
|
// The same block case is special because it's the only time we're looking
|
|
// within a single block to see which instruction comes first. Once we
|
|
// start looking at multiple blocks, the first instruction of the block is
|
|
// reachable, so we only need to determine reachability between whole
|
|
// blocks.
|
|
BasicBlock *BB = const_cast<BasicBlock *>(A->getParent());
|
|
|
|
// If the block is in a loop then we can reach any instruction in the block
|
|
// from any other instruction in the block by going around a backedge.
|
|
if (LI && LI->getLoopFor(BB) != 0)
|
|
return true;
|
|
|
|
// Linear scan, start at 'A', see whether we hit 'B' or the end first.
|
|
for (BasicBlock::const_iterator I = A, E = BB->end(); I != E; ++I) {
|
|
if (&*I == B)
|
|
return true;
|
|
}
|
|
|
|
// Can't be in a loop if it's the entry block -- the entry block may not
|
|
// have predecessors.
|
|
if (BB == &BB->getParent()->getEntryBlock())
|
|
return false;
|
|
|
|
// Otherwise, continue doing the normal per-BB CFG walk.
|
|
for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
|
|
Worklist.push_back(*I);
|
|
|
|
if (Worklist.empty()) {
|
|
// We've proven that there's no path!
|
|
return false;
|
|
}
|
|
} else {
|
|
Worklist.push_back(const_cast<BasicBlock*>(A->getParent()));
|
|
}
|
|
|
|
if (A->getParent() == &A->getParent()->getParent()->getEntryBlock())
|
|
return true;
|
|
if (B->getParent() == &A->getParent()->getParent()->getEntryBlock())
|
|
return false;
|
|
|
|
return isPotentiallyReachableInner(Worklist,
|
|
const_cast<BasicBlock*>(B->getParent()),
|
|
DT, LI);
|
|
}
|