[llvm-commits] CVS: llvm/lib/CodeGen/IfConversion.cpp
Evan Cheng
evan.cheng at apple.com
Fri Jun 8 02:36:23 PDT 2007
Changes in directory llvm/lib/CodeGen:
IfConversion.cpp updated: 1.37 -> 1.38
---
Log message:
Allow more cmp / bcc to be predicated; clean up triangle ifcvt checking code.
---
Diffs of the changes: (+135 -144)
IfConversion.cpp | 279 ++++++++++++++++++++++++++-----------------------------
1 files changed, 135 insertions(+), 144 deletions(-)
Index: llvm/lib/CodeGen/IfConversion.cpp
diff -u llvm/lib/CodeGen/IfConversion.cpp:1.37 llvm/lib/CodeGen/IfConversion.cpp:1.38
--- llvm/lib/CodeGen/IfConversion.cpp:1.37 Thu Jun 7 17:31:28 2007
+++ llvm/lib/CodeGen/IfConversion.cpp Fri Jun 8 04:36:04 2007
@@ -98,13 +98,14 @@
private:
bool ReverseBranchCondition(BBInfo &BBI);
- bool BlockModifyPredicate(MachineBasicBlock *BB) const;
- bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI) const;
+ bool ValidSimple(BBInfo &TrueBBI) const;
+ bool ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
+ bool FalseBranch = false) const;
bool ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const;
- void StructuralAnalysis(MachineBasicBlock *BB);
- bool FeasibilityAnalysis(BBInfo &BBI,
- std::vector<MachineOperand> &Cond,
- bool IgnoreTerm = false);
+ void ScanInstructions(BBInfo &BBI);
+ void AnalyzeBlock(MachineBasicBlock *BB);
+ bool FeasibilityAnalysis(BBInfo &BBI, std::vector<MachineOperand> &Cond,
+ bool isTriangle = false, bool RevBranch = false);
bool AttemptRestructuring(BBInfo &BBI);
bool AnalyzeBlocks(MachineFunction &MF,
std::vector<BBInfo*> &Candidates);
@@ -235,47 +236,44 @@
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;
+/// ValidSimple - Returns true if the 'true' block (along with its
+/// predecessor) forms a valid simple shape for ifcvt.
+bool IfConverter::ValidSimple(BBInfo &TrueBBI) const {
+ return !blockAlwaysFallThrough(TrueBBI) &&
+ TrueBBI.BrCond.size() == 0 && TrueBBI.BB->pred_size() == 1;
}
-/// ValidTriangle - Returns true if the 'true' and 'false' blocks paths (along
+/// ValidTriangle - Returns true if the 'true' and 'false' blocks (along
/// with their common predecessor) forms a valid triangle shape for ifcvt.
-bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI) const {
+bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
+ bool FalseBranch) const {
if (TrueBBI.BB->pred_size() != 1)
return false;
- MachineBasicBlock *TTBB = TrueBBI.TrueBB;
- if (!TTBB && blockAlwaysFallThrough(TrueBBI)) {
+ MachineBasicBlock *TExit = FalseBranch ? TrueBBI.FalseBB : TrueBBI.TrueBB;
+ if (!TExit && blockAlwaysFallThrough(TrueBBI)) {
MachineFunction::iterator I = TrueBBI.BB;
if (++I == TrueBBI.BB->getParent()->end())
return false;
- TTBB = I;
+ TExit = I;
}
- return TTBB && TTBB == FalseBBI.BB;
+ return TExit && TExit == FalseBBI.BB;
}
-/// ValidDiamond - Returns true if the 'true' and 'false' blocks paths (along
+/// ValidDiamond - Returns true if the 'true' and 'false' blocks (along
/// with their common predecessor) forms a valid diamond shape for ifcvt.
bool IfConverter::ValidDiamond(BBInfo &TrueBBI, BBInfo &FalseBBI) const {
+ // FIXME: Also look for fallthrough
return (TrueBBI.TrueBB == FalseBBI.TrueBB &&
TrueBBI.BB->pred_size() == 1 &&
FalseBBI.BB->pred_size() == 1 &&
- !(TrueBBI.ModifyPredicate && FalseBBI.ModifyPredicate) &&
!TrueBBI.FalseBB && !FalseBBI.FalseBB);
}
-/// StructuralAnalysis - Analyze the structure of the sub-CFG starting from
+/// AnalyzeBlock - Analyze the structure of the sub-CFG starting from
/// the specified block. Record its successors and whether it looks like an
/// if-conversion candidate.
-void IfConverter::StructuralAnalysis(MachineBasicBlock *BB) {
+void IfConverter::AnalyzeBlock(MachineBasicBlock *BB) {
BBInfo &BBI = BBAnalysis[BB->getNumber()];
if (BBI.Kind == ICReAnalyze) {
@@ -286,7 +284,6 @@
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.
@@ -301,7 +298,7 @@
if (BBI.TrueBB == BB || BBI.FalseBB == BB)
return;
- StructuralAnalysis(BBI.TrueBB);
+ AnalyzeBlock(BBI.TrueBB);
BBInfo &TrueBBI = BBAnalysis[BBI.TrueBB->getNumber()];
// No false branch. This BB must end with a conditional branch and a
@@ -310,7 +307,7 @@
BBI.FalseBB = findFalseBlock(BB, BBI.TrueBB);
assert(BBI.FalseBB && "Expected to find the fallthrough block!");
- StructuralAnalysis(BBI.FalseBB);
+ AnalyzeBlock(BBI.FalseBB);
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
// If both paths are dead, then forget about it.
@@ -323,34 +320,11 @@
// the CFG to form a triangle with the 'false' path.
std::vector<MachineOperand> RevCond(BBI.BrCond);
bool CanRevCond = !TII->ReverseBranchCondition(RevCond);
- if (FalseBBI.FalseBB) {
- if (TrueBBI.TrueBB && TrueBBI.TrueBB == BBI.FalseBB)
- return;
- std::vector<MachineOperand> Cond(BBI.BrCond);
- if (CanRevCond &&
- FalseBBI.TrueBB && FalseBBI.BB->pred_size() == 1 &&
- FeasibilityAnalysis(FalseBBI, RevCond, true)) {
- std::vector<MachineOperand> FalseCond(FalseBBI.BrCond);
- if (FalseBBI.TrueBB == BBI.TrueBB &&
- TII->SubsumesPredicate(FalseCond, BBI.BrCond)) {
- // Reverse 'true' and 'false' paths.
- ReverseBranchCondition(BBI);
- BBI.Kind = ICTriangle;
- FalseBBI.Kind = ICChild;
- } else if (FalseBBI.FalseBB == BBI.TrueBB &&
- !TII->ReverseBranchCondition(FalseCond) &&
- TII->SubsumesPredicate(FalseCond, BBI.BrCond)) {
- // Reverse 'false' block's 'true' and 'false' paths and then
- // reverse 'true' and 'false' paths.
- ReverseBranchCondition(FalseBBI);
- ReverseBranchCondition(BBI);
- BBI.Kind = ICTriangle;
- FalseBBI.Kind = ICChild;
- }
- }
- } else if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI) &&
- FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
- FeasibilityAnalysis(FalseBBI, RevCond)) {
+
+ if (CanRevCond && ValidDiamond(TrueBBI, FalseBBI) &&
+ !(TrueBBI.ModifyPredicate && FalseBBI.ModifyPredicate) &&
+ FeasibilityAnalysis(TrueBBI, BBI.BrCond) &&
+ FeasibilityAnalysis(FalseBBI, RevCond)) {
// Diamond:
// EBB
// / \_
@@ -364,50 +338,46 @@
BBI.TailBB = TrueBBI.TrueBB;
} else {
// FIXME: Consider duplicating if BB is small.
- bool TryTriangle = ValidTriangle(TrueBBI, FalseBBI);
- bool TrySimple = !blockAlwaysFallThrough(TrueBBI) &&
- TrueBBI.BrCond.size() == 0 && TrueBBI.BB->pred_size() == 1;
- if ((TryTriangle || TrySimple) &&
- FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
- if (TryTriangle) {
- // Triangle:
- // EBB
- // | \_
- // | |
- // | TBB
- // | /
- // FBB
- BBI.Kind = ICTriangle;
- TrueBBI.Kind = ICChild;
- } else {
- // Simple (split, no rejoin):
- // EBB
- // | \_
- // | |
- // | TBB---> exit
- // |
- // FBB
- BBI.Kind = ICSimple;
- TrueBBI.Kind = ICChild;
- }
- } else if (FalseBBI.BrCond.size() == 0 && FalseBBI.BB->pred_size() == 1) {
+ if (ValidTriangle(TrueBBI, FalseBBI) &&
+ FeasibilityAnalysis(TrueBBI, BBI.BrCond, true)) {
+ // Triangle:
+ // EBB
+ // | \_
+ // | |
+ // | TBB
+ // | /
+ // FBB
+ BBI.Kind = ICTriangle;
+ TrueBBI.Kind = ICChild;
+ } else if (ValidSimple(TrueBBI) &&
+ FeasibilityAnalysis(TrueBBI, BBI.BrCond)) {
+ // Simple (split, no rejoin):
+ // EBB
+ // | \_
+ // | |
+ // | TBB---> exit
+ // |
+ // FBB
+ BBI.Kind = ICSimple;
+ TrueBBI.Kind = ICChild;
+ } else if (CanRevCond) {
// Try the other path...
- bool TryTriangle = ValidTriangle(FalseBBI, TrueBBI);
- bool TrySimple = !blockAlwaysFallThrough(FalseBBI);
- if (TryTriangle || TrySimple) {
- std::vector<MachineOperand> RevCond(BBI.BrCond);
- if (!TII->ReverseBranchCondition(RevCond) &&
- FeasibilityAnalysis(FalseBBI, RevCond)) {
- if (TryTriangle) {
- // Reverse 'true' and 'false' paths.
- ReverseBranchCondition(BBI);
- BBI.Kind = ICTriangle;
- FalseBBI.Kind = ICChild;
- } else {
- BBI.Kind = ICSimpleFalse;
- FalseBBI.Kind = ICChild;
- }
- }
+ if (ValidTriangle(FalseBBI, TrueBBI) &&
+ FeasibilityAnalysis(FalseBBI, RevCond, true)) {
+ // Reverse 'true' and 'false' paths.
+ ReverseBranchCondition(BBI);
+ BBI.Kind = ICTriangle;
+ FalseBBI.Kind = ICChild;
+ } else if (ValidTriangle(FalseBBI, TrueBBI, true) &&
+ FeasibilityAnalysis(FalseBBI, RevCond, true, true)) {
+ ReverseBranchCondition(FalseBBI);
+ ReverseBranchCondition(BBI);
+ BBI.Kind = ICTriangle;
+ FalseBBI.Kind = ICChild;
+ } else if (ValidSimple(FalseBBI) &&
+ FeasibilityAnalysis(FalseBBI, RevCond)) {
+ BBI.Kind = ICSimpleFalse;
+ FalseBBI.Kind = ICChild;
}
}
}
@@ -418,11 +388,10 @@
/// cases, that means all the instructions in the block has M_PREDICABLE flag.
/// Also checks if the block contains any instruction which can clobber a
/// predicate (e.g. condition code register). If so, the block is not
-/// predicable unless it's the last instruction. If IgnoreTerm is true then
-/// all the terminator instructions are skipped.
+/// predicable unless it's the last instruction.
bool IfConverter::FeasibilityAnalysis(BBInfo &BBI,
- std::vector<MachineOperand> &Cond,
- bool IgnoreTerm) {
+ std::vector<MachineOperand> &Pred,
+ bool isTriangle, bool RevBranch) {
// If the block is dead, or it is going to be the entry block of a sub-CFG
// that will be if-converted, then it cannot be predicated.
if (BBI.Kind != ICNotAnalyzed &&
@@ -436,13 +405,46 @@
// If it is already predicated, check if its predicate subsumes the new
// predicate.
- if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Cond))
+ if (BBI.Predicate.size() && !TII->SubsumesPredicate(BBI.Predicate, Pred))
return false;
+ bool SeenPredMod = false;
+ bool SeenCondBr = false;
for (MachineBasicBlock::iterator I = BBI.BB->begin(), E = BBI.BB->end();
I != E; ++I) {
- if (IgnoreTerm && TII->isTerminatorInstr(I->getOpcode()))
- continue;
+ const TargetInstrDescriptor *TID = I->getInstrDescriptor();
+ if (SeenPredMod) {
+ // Predicate modification instruction should end the block (except for
+ // already predicated instructions and end of block branches).
+ if (!TII->isPredicated(I)) {
+ // This is the 'true' block of a triangle, i.e. its 'true' block is
+ // the same as the 'false' block of the entry. So false positive
+ // is ok.
+ if (isTriangle && !SeenCondBr && BBI.IsAnalyzable &&
+ (TID->Flags & M_BRANCH_FLAG) != 0 &&
+ (TID->Flags & M_BARRIER_FLAG) == 0) {
+ // This is the first conditional branch, test predicate subsumsion.
+ std::vector<MachineOperand> RevPred(Pred);
+ std::vector<MachineOperand> Cond(BBI.BrCond);
+ if (RevBranch) {
+ if (TII->ReverseBranchCondition(Cond))
+ return false;
+ }
+ if (TII->ReverseBranchCondition(RevPred) ||
+ !TII->SubsumesPredicate(Cond, RevPred))
+ return false;
+ SeenCondBr = true;
+ continue; // Conditional branches is not predicable.
+ }
+ return false;
+ }
+ }
+
+ if (TID->Flags & M_CLOBBERS_PRED) {
+ BBI.ModifyPredicate = true;
+ SeenPredMod = true;
+ }
+
if (!I->isPredicable())
return false;
}
@@ -488,7 +490,7 @@
for (idf_ext_iterator<MachineBasicBlock*> I=idf_ext_begin(Roots[i],Visited),
E = idf_ext_end(Roots[i], Visited); I != E; ++I) {
MachineBasicBlock *BB = *I;
- StructuralAnalysis(BB);
+ AnalyzeBlock(BB);
BBInfo &BBI = BBAnalysis[BB->getNumber()];
switch (BBI.Kind) {
case ICSimple:
@@ -560,23 +562,23 @@
// to the 'false' branch.
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
MergeBlocks(BBI, *CvtBBI);
+ BBI.BB->removeSuccessor(CvtBBI->BB);
bool IterIfcvt = true;
if (!isNextBlock(BBI.BB, NextBBI->BB)) {
InsertUncondBranch(BBI.BB, NextBBI->BB, TII);
BBI.hasFallThrough = false;
- 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;
+ // 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));
@@ -610,45 +612,34 @@
TII->InsertBranch(*BBI.TrueBB, TrueBBI.FalseBB, NULL, RevCond);
}
- // Join the 'true' and 'false' blocks if the 'false' block has no other
- // predecessors. Otherwise, add a unconditional branch from 'true' to 'false'.
+ // Now merge the entry of the triangle with the true block.
+ BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
+ MergeBlocks(BBI, TrueBBI);
+
+ // Merge in the 'false' block if the 'false' block has no other
+ // predecessors. Otherwise, add a unconditional branch from to 'false'.
BBInfo &FalseBBI = BBAnalysis[BBI.FalseBB->getNumber()];
bool FalseBBDead = false;
bool IterIfcvt = true;
- bool isFallThrough = isNextBlock(TrueBBI.BB, FalseBBI.BB);
+ bool isFallThrough = isNextBlock(BBI.BB, FalseBBI.BB);
if (!isFallThrough) {
// Only merge them if the true block does not fallthrough to the false
// block. By not merging them, we make it possible to iteratively
// ifcvt the blocks.
- if (!HasEarlyExit && FalseBBI.BB->pred_size() == 2) {
- MergeBlocks(TrueBBI, FalseBBI);
+ if (!HasEarlyExit && FalseBBI.BB->pred_size() == 1) {
+ MergeBlocks(BBI, FalseBBI);
FalseBBDead = true;
- // Mixed predicated and unpredicated code. This cannot be iteratively
- // predicated.
- IterIfcvt = false;
} else {
- InsertUncondBranch(TrueBBI.BB, FalseBBI.BB, TII);
+ InsertUncondBranch(BBI.BB, FalseBBI.BB, TII);
TrueBBI.hasFallThrough = 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;
}
+ // Mixed predicated and unpredicated code. This cannot be iteratively
+ // predicated.
+ IterIfcvt = false;
}
- // Now merge the entry of the triangle with the true block.
- BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
- MergeBlocks(BBI, TrueBBI);
// Remove entry to false edge if false block is merged in as well.
- if (FalseBBDead && BBI.BB->isSuccessor(FalseBBI.BB))
+ if (FalseBBDead)
BBI.BB->removeSuccessor(FalseBBI.BB);
std::copy(BBI.BrCond.begin(), BBI.BrCond.end(),
std::back_inserter(BBI.Predicate));
More information about the llvm-commits
mailing list