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* Finish the implementation of isEdgeFeasible this fixes bug:

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test/Regression/Transforms/SCCP/2002-05-02-EdgeFailure.ll
* SCCP now preserves the CFG:  It leaves conditional branches the way they
  are in the program, not simplifying them.  A seperate pass should eliminate
  the potentially dead basic blocks and edges in the CFG.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2446 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2002-05-02 21:44:00 +00:00
parent 59f0ce2a41
commit b9a6634466
1 changed files with 77 additions and 57 deletions
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134
lib/Transforms/Scalar/SCCP.cpp
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@ -6,7 +6,7 @@
// * Assumes values are constant unless proven otherwise
// * Assumes BasicBlocks are dead unless proven otherwise
// * Proves values to be constant, and replaces them with constants
// . Proves conditional branches constant, and unconditionalizes them
// * Proves conditional branches constant, and unconditionalizes them
// * Folds multiple identical constants in the constant pool together
//
// Notice that:
@ -106,8 +106,7 @@ public:
bool runOnFunction(Function *F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
// FIXME: SCCP does not preserve the CFG because it folds terminators!
//AU.preservesCFG();
AU.preservesCFG();
}
@ -184,9 +183,7 @@ private:
// Terminators
void visitReturnInst(ReturnInst *I) { /*does not have an effect*/ }
void visitBranchInst(BranchInst *I);
void visitInvokeInst(InvokeInst *I);
void visitSwitchInst(SwitchInst *I);
void visitTerminatorInst(TerminatorInst *TI);
void visitUnaryOperator(Instruction *I);
void visitCastInst(CastInst *I) { visitUnaryOperator(I); }
@ -207,6 +204,11 @@ private:
markOverdefined(I); // Just in case
}
// getFeasibleSuccessors - Return a vector of booleans to indicate which
// successors are reachable from a given terminator instruction.
//
void getFeasibleSuccessors(TerminatorInst *I, std::vector<bool> &Succs);
// isEdgeFeasible - Return true if the control flow edge from the 'From' basic
// block to the 'To' basic block is currently feasible...
//
@ -312,15 +314,9 @@ bool SCCP::runOnFunction(Function *F) {
// Hey, we just changed something!
MadeChanges = true;
// Do NOT advance the iterator, skipping the next instruction...
continue;
} else if (TerminatorInst *TI = dyn_cast<TerminatorInst>(Inst)) {
MadeChanges |= ConstantFoldTerminator(BB, BI, TI);
} else {
++BI;
}
++BI;
}
}
@ -331,6 +327,54 @@ bool SCCP::runOnFunction(Function *F) {
return MadeChanges;
}
// getFeasibleSuccessors - Return a vector of booleans to indicate which
// successors are reachable from a given terminator instruction.
//
void SCCP::getFeasibleSuccessors(TerminatorInst *TI, std::vector<bool> &Succs) {
assert(Succs.size() == TI->getNumSuccessors() && "Succs vector wrong size!");
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
if (BI->isUnconditional()) {
Succs[0] = true;
} else {
InstVal &BCValue = getValueState(BI->getCondition());
if (BCValue.isOverdefined()) {
// Overdefined condition variables mean the branch could go either way.
Succs[0] = Succs[1] = true;
} else if (BCValue.isConstant()) {
// Constant condition variables mean the branch can only go a single way
Succs[BCValue.getConstant() == ConstantBool::False] = true;
}
}
} else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
// Invoke instructions successors are always executable.
Succs[0] = Succs[1] = true;
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
InstVal &SCValue = getValueState(SI->getCondition());
if (SCValue.isOverdefined()) { // Overdefined condition?
// All destinations are executable!
Succs.assign(TI->getNumSuccessors(), true);
} else if (SCValue.isConstant()) {
Constant *CPV = SCValue.getConstant();
// Make sure to skip the "default value" which isn't a value
for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
Succs[i] = true;
return;
}
}
// Constant value not equal to any of the branches... must execute
// default branch then...
Succs[0] = true;
}
} else {
cerr << "SCCP: Don't know how to handle: " << TI;
Succs.assign(TI->getNumSuccessors(), true);
}
}
// isEdgeFeasible - Return true if the control flow edge from the 'From' basic
// block to the 'To' basic block is currently feasible...
//
@ -340,8 +384,18 @@ bool SCCP::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
// Make sure the source basic block is executable!!
if (!BBExecutable.count(From)) return false;
// This should check the terminator in From!
return true;
// Check to make sure this edge itself is actually feasible now...
TerminatorInst *FT = From->getTerminator();
std::vector<bool> SuccFeasible(FT->getNumSuccessors());
getFeasibleSuccessors(FT, SuccFeasible);
// Check all edges from From to To. If any are feasible, return true.
for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
if (FT->getSuccessor(i) == To && SuccFeasible[i])
return true;
// Otherwise, none of the edges are actually feasible at this time...
return false;
}
// visit Implementations - Something changed in this instruction... Either an
@ -412,48 +466,14 @@ void SCCP::visitPHINode(PHINode *PN) {
}
}
void SCCP::visitBranchInst(BranchInst *BI) {
if (BI->isUnconditional())
return; // Unconditional branches are already handled!
void SCCP::visitTerminatorInst(TerminatorInst *TI) {
std::vector<bool> SuccFeasible(TI->getNumSuccessors());
getFeasibleSuccessors(TI, SuccFeasible);
InstVal &BCValue = getValueState(BI->getCondition());
if (BCValue.isOverdefined()) {
// Overdefined condition variables mean the branch could go either way.
markExecutable(BI->getSuccessor(0));
markExecutable(BI->getSuccessor(1));
} else if (BCValue.isConstant()) {
// Constant condition variables mean the branch can only go a single way.
if (BCValue.getConstant() == ConstantBool::True)
markExecutable(BI->getSuccessor(0));
else
markExecutable(BI->getSuccessor(1));
}
}
void SCCP::visitInvokeInst(InvokeInst *II) {
markExecutable(II->getNormalDest());
markExecutable(II->getExceptionalDest());
}
void SCCP::visitSwitchInst(SwitchInst *SI) {
InstVal &SCValue = getValueState(SI->getCondition());
if (SCValue.isOverdefined()) { // Overdefined condition? All dests are exe
for(unsigned i = 0, E = SI->getNumSuccessors(); i != E; ++i)
markExecutable(SI->getSuccessor(i));
} else if (SCValue.isConstant()) {
Constant *CPV = SCValue.getConstant();
// Make sure to skip the "default value" which isn't a value
for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
markExecutable(SI->getSuccessor(i));
return;
}
}
// Constant value not equal to any of the branches... must execute
// default branch then...
markExecutable(SI->getDefaultDest());
}
// Mark all feasible successors executable...
for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
if (SuccFeasible[i])
markExecutable(TI->getSuccessor(i));
}
void SCCP::visitUnaryOperator(Instruction *I) {