[llvm-commits] CVS: llvm/lib/CodeGen/IfConversion.cpp
Evan Cheng
evan.cheng at apple.com
Wed Jun 6 03:16:39 PDT 2007
Changes in directory llvm/lib/CodeGen:
IfConversion.cpp updated: 1.32 -> 1.33
---
Log message:
Lots of bug fixes.
---
Diffs of the changes: (+76 -40)
IfConversion.cpp | 116 ++++++++++++++++++++++++++++++++++++-------------------
1 files changed, 76 insertions(+), 40 deletions(-)
Index: llvm/lib/CodeGen/IfConversion.cpp
diff -u llvm/lib/CodeGen/IfConversion.cpp:1.32 llvm/lib/CodeGen/IfConversion.cpp:1.33
--- llvm/lib/CodeGen/IfConversion.cpp:1.32 Tue Jun 5 21:08:52 2007
+++ llvm/lib/CodeGen/IfConversion.cpp Wed Jun 6 05:16:17 2007
@@ -41,7 +41,7 @@
ICTriangle, // BB is entry of a triangle sub-CFG.
ICDiamond, // BB is entry of a diamond sub-CFG.
ICChild, // BB is part of the sub-CFG that'll be predicated.
- ICDead // BB has been converted and merged, it's now dead.
+ ICDead // BB cannot be if-converted again.
};
/// BBInfo - One per MachineBasicBlock, this is used to cache the result
@@ -54,8 +54,8 @@
/// Kind - Type of block. See BBICKind.
/// NonPredSize - Number of non-predicated instructions.
/// IsAnalyzable - True if AnalyzeBranch() returns false.
- /// ModifyPredicate - FIXME: Not used right now. True if BB would modify
- /// the predicate (e.g. has cmp, call, etc.)
+ /// ModifyPredicate - True if BB would modify the predicate (e.g. has
+ /// cmp, call, etc.)
/// BB - Corresponding MachineBasicBlock.
/// TrueBB / FalseBB- See AnalyzeBranch().
/// BrCond - Conditions for end of block conditional branches.
@@ -96,6 +96,7 @@
private:
bool ReverseBranchCondition(BBInfo &BBI);
+ bool BlockModifyPredicate(MachineBasicBlock *BB) const;
void StructuralAnalysis(MachineBasicBlock *BB);
bool FeasibilityAnalysis(BBInfo &BBI,
std::vector<MachineOperand> &Cond,
@@ -112,6 +113,11 @@
bool IgnoreTerm = false);
void MergeBlocks(BBInfo &TrueBBI, BBInfo &FalseBBI);
+ // blockFallsThrough - Block ends without a terminator.
+ bool blockFallsThrough(BBInfo &BBI) const {
+ return BBI.IsAnalyzable && BBI.TrueBB == NULL;
+ }
+
// IfcvtCandidateCmp - Used to sort if-conversion candidates.
static bool IfcvtCandidateCmp(BBInfo* C1, BBInfo* C2){
// Favor diamond over triangle, etc.
@@ -161,7 +167,9 @@
case ICSimpleFalse: {
bool isRev = BBI.Kind == ICSimpleFalse;
DOUT << "Ifcvt (Simple" << (BBI.Kind == ICSimpleFalse ? " false" : "")
- << "): BB#" << BBI.BB->getNumber() << " ";
+ << "): BB#" << BBI.BB->getNumber() << " ("
+ << ((BBI.Kind == ICSimpleFalse)
+ ? BBI.FalseBB->getNumber() : BBI.TrueBB->getNumber()) << ") ";
RetVal = IfConvertSimple(BBI);
DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
if (RetVal)
@@ -170,13 +178,19 @@
break;
}
case ICTriangle:
- DOUT << "Ifcvt (Triangle): BB#" << BBI.BB->getNumber() << " ";
+ DOUT << "Ifcvt (Triangle): BB#" << BBI.BB->getNumber() << " (T:"
+ << BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber()
+ << ") ";
RetVal = IfConvertTriangle(BBI);
DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
if (RetVal) NumTriangle++;
break;
case ICDiamond:
- DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " ";
+ DOUT << "Ifcvt (Diamond): BB#" << BBI.BB->getNumber() << " (T:"
+ << BBI.TrueBB->getNumber() << ",F:" << BBI.FalseBB->getNumber();
+ if (BBI.TailBB)
+ DOUT << "," << BBI.TailBB->getNumber() ;
+ DOUT << ") ";
RetVal = IfConvertDiamond(BBI);
DOUT << (RetVal ? "succeeded!" : "failed!") << "\n";
if (RetVal) NumDiamonds++;
@@ -217,6 +231,17 @@
return false;
}
+/// BlockModifyPredicate - Returns true if any instruction in the block may
+/// clobber the condition code or register(s) used to predicate instructions,
+/// e.g. call, cmp.
+bool IfConverter::BlockModifyPredicate(MachineBasicBlock *BB) const {
+ for (MachineBasicBlock::const_reverse_iterator I = BB->rbegin(),
+ E = BB->rend(); I != E; ++I)
+ if (I->getInstrDescriptor()->Flags & M_CLOBBERS_PRED)
+ return true;
+ return false;
+}
+
/// StructuralAnalysis - Analyze the structure of the sub-CFG starting from
/// the specified block. Record its successors and whether it looks like an
/// if-conversion candidate.
@@ -231,6 +256,7 @@
return; // Already analyzed.
BBI.BB = BB;
BBI.NonPredSize = std::distance(BB->begin(), BB->end());
+ BBI.ModifyPredicate = BlockModifyPredicate(BB);
}
// Look for 'root' of a simple (non-nested) triangle or diamond.
@@ -254,7 +280,13 @@
StructuralAnalysis(BBI.FalseBB);
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
-
+
+ // If both paths are dead, then forget about it.
+ if (TrueBBI.Kind == ICDead && FalseBBI.Kind == ICDead) {
+ BBI.Kind = ICDead;
+ return;
+ }
+
// Look for more opportunities to if-convert a triangle. Try to restructure
// the CFG to form a triangle with the 'false' path.
std::vector<MachineOperand> RevCond(BBI.BrCond);
@@ -337,11 +369,12 @@
}
} else if (FalseBBI.BrCond.size() == 0 && FalseBBI.BB->pred_size() == 1) {
// Try the other path...
+ bool TryTriangle = FalseBBI.TrueBB && FalseBBI.TrueBB == BBI.TrueBB &&
+ FalseBBI.BB->pred_size() == 1;
std::vector<MachineOperand> RevCond(BBI.BrCond);
if (!TII->ReverseBranchCondition(RevCond) &&
FeasibilityAnalysis(FalseBBI, RevCond)) {
- if (FalseBBI.TrueBB && FalseBBI.TrueBB == BBI.TrueBB &&
- FalseBBI.BB->pred_size() == 1) {
+ if (TryTriangle) {
// Reverse 'true' and 'false' paths.
ReverseBranchCondition(BBI);
BBI.Kind = ICTriangle;
@@ -486,17 +519,13 @@
/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
///
bool IfConverter::IfConvertSimple(BBInfo &BBI) {
- bool ReverseCond = BBI.Kind == ICSimpleFalse;
-
- BBI.Kind = ICNotClassfied;
-
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
BBInfo *CvtBBI = &TrueBBI;
BBInfo *NextBBI = &FalseBBI;
std::vector<MachineOperand> Cond(BBI.BrCond);
- if (ReverseCond) {
+ if (BBI.Kind == ICSimpleFalse) {
std::swap(CvtBBI, NextBBI);
TII->ReverseBranchCondition(Cond);
}
@@ -517,23 +546,27 @@
MergeBlocks(BBI, *CvtBBI);
bool IterIfcvt = true;
if (!isNextBlock(BBI.BB, NextBBI->BB)) {
- // Now ifcvt'd block will look like this:
- // BB:
- // ...
- // t, f = cmp
- // if t op
- // b BBf
- //
- // We cannot further ifcvt this block because the unconditional branch will
- // have to be predicated on the new condition, that will not be available
- // if cmp executes.
InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
+ if (BBI.ModifyPredicate)
+ // Now ifcvt'd block will look like this:
+ // BB:
+ // ...
+ // t, f = cmp
+ // if t op
+ // b BBf
+ //
+ // We cannot further ifcvt this block because the unconditional branch will
+ // have to be predicated on the new condition, that will not be available
+ // if cmp executes.
+ IterIfcvt = false;
}
std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
// Update block info. BB can be iteratively if-converted.
if (IterIfcvt)
BBI.Kind = ICReAnalyze;
+ else
+ BBI.Kind = ICDead;
ReTryPreds(BBI.BB);
CvtBBI->Kind = ICDead;
@@ -544,8 +577,6 @@
/// IfConvertTriangle - If convert a triangle sub-CFG.
///
bool IfConverter::IfConvertTriangle(BBInfo &BBI) {
- BBI.Kind = ICNotClassfied;
-
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
// Predicate the 'true' block after removing its branch.
@@ -571,17 +602,18 @@
FalseBBDead = true;
} else if (!isNextBlock(TrueBBI.BB, FalseBBI.BB)) {
InsertUncondBranch(TrueBBI.BB, FalseBBI.BB, TII);
- // Now ifcvt'd block will look like this:
- // BB:
- // ...
- // t, f = cmp
- // if t op
- // b BBf
- //
- // We cannot further ifcvt this block because the unconditional branch will
- // have to be predicated on the new condition, that will not be available
- // if cmp executes.
- IterIfcvt = false;
+ if (BBI.ModifyPredicate || TrueBBI.ModifyPredicate)
+ // Now ifcvt'd block will look like this:
+ // BB:
+ // ...
+ // t, f = cmp
+ // if t op
+ // b BBf
+ //
+ // We cannot further ifcvt this block because the unconditional branch will
+ // have to be predicated on the new condition, that will not be available
+ // if cmp executes.
+ IterIfcvt = false;
}
// Now merge the entry of the triangle with the true block.
@@ -593,6 +625,8 @@
// Update block info. BB can be iteratively if-converted.
if (IterIfcvt)
BBI.Kind = ICReAnalyze;
+ else
+ BBI.Kind = ICDead;
ReTryPreds(BBI.BB);
TrueBBI.Kind = ICDead;
if (FalseBBDead)
@@ -605,8 +639,6 @@
/// IfConvertDiamond - If convert a diamond sub-CFG.
///
bool IfConverter::IfConvertDiamond(BBInfo &BBI) {
- BBI.Kind = ICNotClassfied;
-
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
@@ -714,6 +746,7 @@
}
// Update block info.
+ BBI.Kind = ICDead;
TrueBBI.Kind = ICDead;
FalseBBI.Kind = ICDead;
@@ -785,7 +818,10 @@
// Transfer preds / succs and update size.
TransferPreds(ToBBI.BB, FromBBI.BB);
- TransferSuccs(ToBBI.BB, FromBBI.BB);
+ if (!blockFallsThrough(FromBBI.BB))
+ TransferSuccs(ToBBI.BB, FromBBI.BB);
ToBBI.NonPredSize += FromBBI.NonPredSize;
FromBBI.NonPredSize = 0;
+
+ ToBBI.ModifyPredicate |= FromBBI.ModifyPredicate;
}
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