[llvm-commits] [llvm] r53526 - /llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
Chris Lattner
sabre at nondot.org
Sun Jul 13 14:12:01 PDT 2008
Author: lattner
Date: Sun Jul 13 16:12:01 2008
New Revision: 53526
URL: http://llvm.org/viewvc/llvm-project?rev=53526&view=rev
Log:
Refactor some code out into its own helper function, getting rid of crazy multiline
conditionals and commenting the code better.
No functionality change.
Modified:
llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=53526&r1=53525&r2=53526&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Sun Jul 13 16:12:01 2008
@@ -1425,6 +1425,86 @@
return true;
}
+/// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
+/// and if a predecessor branches to us and one of our successors, fold the
+/// setcc into the predecessor and use logical operations to pick the right
+/// destination.
+static bool FoldBranchToCommonDest(BranchInst *BI) {
+ Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
+ if (Cond == 0) return false;
+
+ BasicBlock *BB = BI->getParent();
+
+ // Only allow this if the condition is a simple instruction that can be
+ // executed unconditionally. It must be in the same block as the branch, and
+ // must be at the front of the block.
+ if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
+ Cond->getParent() != BB || &BB->front() != Cond || !Cond->hasOneUse())
+ return false;
+
+ // Make sure the instruction after the condition is the cond branch.
+ BasicBlock::iterator CondIt = Cond; ++CondIt;
+ if (&*CondIt != BI)
+ return false;
+
+ // Finally, don't infinitely unroll conditional loops.
+ BasicBlock *TrueDest = BI->getSuccessor(0);
+ BasicBlock *FalseDest = BI->getSuccessor(1);
+ if (TrueDest == BB || FalseDest == BB)
+ return false;
+
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+ BasicBlock *PredBlock = *PI;
+ BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
+ if (PBI == 0 || PBI->isUnconditional() ||
+ !SafeToMergeTerminators(BI, PBI))
+ continue;
+
+ // Canonicalize the predecessors condition (inverting it) if needed to allow
+ // this xform to trigger.
+ if (PBI->getSuccessor(0) == FalseDest ||
+ PBI->getSuccessor(1) == TrueDest) {
+ Value *NewCond =
+ BinaryOperator::CreateNot(PBI->getCondition(),
+ PBI->getCondition()->getName()+".not", PBI);
+ PBI->setCondition(NewCond);
+ BasicBlock *OldTrue = PBI->getSuccessor(0);
+ BasicBlock *OldFalse = PBI->getSuccessor(1);
+ PBI->setSuccessor(0, OldFalse);
+ PBI->setSuccessor(1, OldTrue);
+ }
+
+ if ((PBI->getSuccessor(0) == TrueDest && FalseDest != BB) ||
+ (PBI->getSuccessor(1) == FalseDest && TrueDest != BB)) {
+ // Clone Cond into the predecessor basic block, and or/and the
+ // two conditions together.
+ Instruction *New = Cond->clone();
+ PredBlock->getInstList().insert(PBI, New);
+ New->takeName(Cond);
+ Cond->setName(New->getName()+".old");
+
+ Value *NewCond;
+ if (PBI->getSuccessor(0) == TrueDest)
+ NewCond = BinaryOperator::CreateOr(PBI->getCondition(), New, "or.cond",
+ PBI);
+ else
+ NewCond = BinaryOperator::CreateOr(PBI->getCondition(), New, "and.cond",
+ PBI);
+ PBI->setCondition(NewCond);
+ if (PBI->getSuccessor(0) == BB) {
+ AddPredecessorToBlock(TrueDest, PredBlock, BB);
+ PBI->setSuccessor(0, TrueDest);
+ }
+ if (PBI->getSuccessor(1) == BB) {
+ AddPredecessorToBlock(FalseDest, PredBlock, BB);
+ PBI->setSuccessor(1, FalseDest);
+ }
+ return true;
+ }
+ }
+ return false;
+}
+
namespace {
/// ConstantIntOrdering - This class implements a stable ordering of constant
@@ -1628,7 +1708,7 @@
if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
Succ != BB) // Don't hurt infinite loops!
if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
- return 1;
+ return true;
} else { // Conditional branch
if (isValueEqualityComparison(BI)) {
@@ -1658,59 +1738,9 @@
// If this basic block is ONLY a setcc and a branch, and if a predecessor
// branches to us and one of our successors, fold the setcc into the
// predecessor and use logical operations to pick the right destination.
- BasicBlock *TrueDest = BI->getSuccessor(0);
- BasicBlock *FalseDest = BI->getSuccessor(1);
- if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition())) {
- BasicBlock::iterator CondIt = Cond;
- if ((isa<CmpInst>(Cond) || isa<BinaryOperator>(Cond)) &&
- Cond->getParent() == BB && &BB->front() == Cond &&
- &*++CondIt == BI && Cond->hasOneUse() &&
- TrueDest != BB && FalseDest != BB)
- for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI!=E; ++PI)
- if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
- if (PBI->isConditional() && SafeToMergeTerminators(BI, PBI)) {
- BasicBlock *PredBlock = *PI;
- if (PBI->getSuccessor(0) == FalseDest ||
- PBI->getSuccessor(1) == TrueDest) {
- // Invert the predecessors condition test (xor it with true),
- // which allows us to write this code once.
- Value *NewCond =
- BinaryOperator::CreateNot(PBI->getCondition(),
- PBI->getCondition()->getName()+".not", PBI);
- PBI->setCondition(NewCond);
- BasicBlock *OldTrue = PBI->getSuccessor(0);
- BasicBlock *OldFalse = PBI->getSuccessor(1);
- PBI->setSuccessor(0, OldFalse);
- PBI->setSuccessor(1, OldTrue);
- }
+ if (FoldBranchToCommonDest(BI))
+ return SimplifyCFG(BB) | 1;
- if ((PBI->getSuccessor(0) == TrueDest && FalseDest != BB) ||
- (PBI->getSuccessor(1) == FalseDest && TrueDest != BB)) {
- // Clone Cond into the predecessor basic block, and or/and the
- // two conditions together.
- Instruction *New = Cond->clone();
- PredBlock->getInstList().insert(PBI, New);
- New->takeName(Cond);
- Cond->setName(New->getName()+".old");
- Instruction::BinaryOps Opcode =
- PBI->getSuccessor(0) == TrueDest ?
- Instruction::Or : Instruction::And;
- Value *NewCond =
- BinaryOperator::Create(Opcode, PBI->getCondition(),
- New, "bothcond", PBI);
- PBI->setCondition(NewCond);
- if (PBI->getSuccessor(0) == BB) {
- AddPredecessorToBlock(TrueDest, PredBlock, BB);
- PBI->setSuccessor(0, TrueDest);
- }
- if (PBI->getSuccessor(1) == BB) {
- AddPredecessorToBlock(FalseDest, PredBlock, BB);
- PBI->setSuccessor(1, FalseDest);
- }
- return SimplifyCFG(BB) | 1;
- }
- }
- }
// Scan predessor blocks for conditional branches.
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
@@ -1811,7 +1841,7 @@
DOUT << "FOLDING BRs:" << *PBI->getParent()
<< "AND: " << *BI->getParent();
-
+
// BI may have other predecessors. Because of this, we leave
// it alone, but modify PBI.
More information about the llvm-commits
mailing list