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Merged
merged 2 commits into from
Oct 26, 2020
Merged

Improve SimplifyCFG: remove conditional branches to the same target. #34441

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d82e0ff
SILInliner: Critical edges have no code size impact.
atrick Sep 26, 2018
d8dcf61
Improve SimplifyCFG: remove conditional branches to the same target.
atrick Oct 20, 2020
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38 changes: 28 additions & 10 deletions lib/SILOptimizer/Transforms/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -802,10 +802,12 @@ static int getThreadingCost(SILInstruction *I) {
return 0;
}

static int maxBranchRecursionDepth = 6;
/// couldSimplifyUsers - Check to see if any simplifications are possible if
/// "Val" is substituted for BBArg. If so, return true, if nothing obvious
/// is possible, return false.
static bool couldSimplifyEnumUsers(SILArgument *BBArg, int Budget) {
static bool couldSimplifyEnumUsers(SILArgument *BBArg, int Budget,
int recursionDepth = 0) {
SILBasicBlock *BB = BBArg->getParent();
int BudgetForBranch = 100;

Expand Down Expand Up @@ -833,6 +835,9 @@ static bool couldSimplifyEnumUsers(SILArgument *BBArg, int Budget) {
}

if (auto *BI = dyn_cast<BranchInst>(User)) {
if (recursionDepth >= maxBranchRecursionDepth) {
return false;
}
if (BudgetForBranch > Budget) {
BudgetForBranch = Budget;
for (SILInstruction &I : *BB) {
Expand All @@ -844,7 +849,8 @@ static bool couldSimplifyEnumUsers(SILArgument *BBArg, int Budget) {
if (BudgetForBranch > 0) {
SILBasicBlock *DestBB = BI->getDestBB();
unsigned OpIdx = UI->getOperandNumber();
if (couldSimplifyEnumUsers(DestBB->getArgument(OpIdx), BudgetForBranch))
if (couldSimplifyEnumUsers(DestBB->getArgument(OpIdx), BudgetForBranch,
recursionDepth + 1))
return true;
}
}
Expand Down Expand Up @@ -1565,17 +1571,29 @@ bool SimplifyCFG::simplifyCondBrBlock(CondBranchInst *BI) {

// Simplify cond_br where both sides jump to the same blocks with the same
// args.
if (TrueArgs == FalseArgs && (TrueSide == FalseTrampolineDest ||
FalseSide == TrueTrampolineDest)) {
LLVM_DEBUG(llvm::dbgs() << "replace cond_br with same dests with br: "
<< *BI);
SILBuilderWithScope(BI).createBranch(BI->getLoc(),
TrueTrampolineDest ? FalseSide : TrueSide, TrueArgs);
auto condBrToBr = [&](OperandValueArrayRef branchArgs,
SILBasicBlock *newDest) {
LLVM_DEBUG(llvm::dbgs()
<< "replace cond_br with same dests with br: " << *BI);
SILBuilderWithScope(BI).createBranch(BI->getLoc(), newDest, branchArgs);
BI->eraseFromParent();
addToWorklist(ThisBB);
addToWorklist(TrueSide);
++NumConstantFolded;
return true;
};
if (TrueArgs == FalseArgs) {
if (TrueTrampolineDest) {
if (TrueTrampolineDest == FalseSide
|| TrueTrampolineDest == FalseTrampolineDest) {
condBrToBr(TrueArgs, TrueTrampolineDest);
removeIfDead(TrueSide);
removeIfDead(FalseSide);
return true;
}
} else if (FalseTrampolineDest == TrueSide) {
condBrToBr(TrueArgs, FalseTrampolineDest);
removeIfDead(FalseSide);
return true;
}
}

auto *TrueTrampolineBr = getTrampolineWithoutBBArgsTerminator(TrueSide);
Expand Down
6 changes: 5 additions & 1 deletion lib/SILOptimizer/Utils/SILInliner.cpp
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Expand Up @@ -790,6 +790,11 @@ InlineCost swift::instructionInlineCost(SILInstruction &I) {
case SILInstructionKind::GetAsyncContinuationInst:
return InlineCost::Free;

// Unconditional branch is free in empty blocks.
case SILInstructionKind::BranchInst:
return (I.getIterator() == I.getParent()->begin())
? InlineCost::Free : InlineCost::Expensive;

case SILInstructionKind::AbortApplyInst:
case SILInstructionKind::ApplyInst:
case SILInstructionKind::TryApplyInst:
Expand All @@ -804,7 +809,6 @@ InlineCost swift::instructionInlineCost(SILInstruction &I) {
case SILInstructionKind::WitnessMethodInst:
case SILInstructionKind::AssignInst:
case SILInstructionKind::AssignByWrapperInst:
case SILInstructionKind::BranchInst:
case SILInstructionKind::CheckedCastBranchInst:
case SILInstructionKind::CheckedCastValueBranchInst:
case SILInstructionKind::CheckedCastAddrBranchInst:
Expand Down
36 changes: 18 additions & 18 deletions test/SILOptimizer/inliner_spa.sil
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Original file line number Diff line number Diff line change
Expand Up @@ -19,10 +19,10 @@ bb0:
}

// CHECK-LABEL: SPA @test_if_then_else
// CHECK-NEXT: bb0: length=1+0, d-entry=0, d-exit=2
// CHECK-NEXT: bb0: length=1+0, d-entry=0, d-exit=1
// CHECK-NEXT: bb1: length=3+0, d-entry=1, d-exit=3
// CHECK-NEXT: bb2: length=1+0, d-entry=1, d-exit=1
// CHECK-NEXT: bb3: length=0+0, d-entry=2, d-exit=0
// CHECK-NEXT: bb2: length=0+0, d-entry=1, d-exit=0
// CHECK-NEXT: bb3: length=0+0, d-entry=1, d-exit=0

sil @test_if_then_else : $@convention(thin) () -> () {
bb0:
Expand All @@ -42,9 +42,9 @@ bb3:
}

// CHECK-LABEL: SPA @test_simple_loop
// CHECK-NEXT: bb0: length=1+0, d-entry=0, d-exit=34
// CHECK-NEXT: bb1: length=3+30, d-entry=1, d-exit=33
// CHECK-NEXT: bb2: length=0+0, d-entry=34, d-exit=0
// CHECK-NEXT: bb0: length=0+0, d-entry=0, d-exit=33
// CHECK-NEXT: bb1: length=3+30, d-entry=0, d-exit=33
// CHECK-NEXT: bb2: length=0+0, d-entry=33, d-exit=0
// CHECK-NEXT: Loop bb1:
// CHECK-NEXT: bb1: length=3+0, d-entry=0, d-exit=3

Expand All @@ -64,9 +64,9 @@ bb2:

// CHECK-LABEL: SPA @test_loop_with_bypass_edge
// CHECK-NEXT: bb0: length=1+30, d-entry=0, d-exit=31
// CHECK-NEXT: bb1: length=1+0, d-entry=31, d-exit=5
// CHECK-NEXT: bb2: length=3+0, d-entry=32, d-exit=4
// CHECK-NEXT: bb3: length=1+0, d-entry=35, d-exit=1
// CHECK-NEXT: bb1: length=0+0, d-entry=31, d-exit=3
// CHECK-NEXT: bb2: length=3+0, d-entry=31, d-exit=3
// CHECK-NEXT: bb3: length=0+0, d-entry=34, d-exit=0
// CHECK-NEXT: bb4: length=0+0, d-entry=31, d-exit=0
// CHECK-NEXT: Loop bb2:
// CHECK-NEXT: bb2: length=3+0, d-entry=0, d-exit=3
Expand All @@ -93,12 +93,12 @@ bb4:

// CHECK-LABEL: SPA @test_nested_loops
// CHECK-NEXT: bb0: length=1+40, d-entry=0, d-exit=41
// CHECK-NEXT: bb1: length=1+0, d-entry=41, d-exit=6
// CHECK-NEXT: bb2: length=1+0, d-entry=42, d-exit=5
// CHECK-NEXT: bb3: length=3+0, d-entry=43, d-exit=5
// CHECK-NEXT: bb4: length=2+0, d-entry=43, d-exit=4
// CHECK-NEXT: bb5: length=1+0, d-entry=45, d-exit=2
// CHECK-NEXT: bb6: length=1+0, d-entry=46, d-exit=1
// CHECK-NEXT: bb1: length=0+0, d-entry=41, d-exit=4
// CHECK-NEXT: bb2: length=1+0, d-entry=41, d-exit=4
// CHECK-NEXT: bb3: length=3+0, d-entry=42, d-exit=4
// CHECK-NEXT: bb4: length=2+0, d-entry=42, d-exit=3
// CHECK-NEXT: bb5: length=1+0, d-entry=44, d-exit=1
// CHECK-NEXT: bb6: length=0+0, d-entry=45, d-exit=0
// CHECK-NEXT: bb7: length=0+0, d-entry=41, d-exit=0
// CHECK-NEXT: Loop bb2:
// CHECK-NEXT: bb2: length=1+0, d-entry=0, d-exit=4
Expand Down Expand Up @@ -146,9 +146,9 @@ bb0:
}

// CHECK-LABEL: SPA @test_call_of_noreturn_in_loop
// CHECK-NEXT: bb0: length=1+0, d-entry=0, d-exit=133
// CHECK-NEXT: bb1: length=12+120, d-entry=1, d-exit=132
// CHECK-NEXT: bb2: length=0+0, d-entry=133, d-exit=0
// CHECK-NEXT: bb0: length=0+0, d-entry=0, d-exit=132
// CHECK-NEXT: bb1: length=12+120, d-entry=0, d-exit=132
// CHECK-NEXT: bb2: length=0+0, d-entry=132, d-exit=0
// CHECK-NEXT: Loop bb1:
// CHECK-NEXT: bb1: length=12+0, d-entry=0, d-exit=12
sil @test_call_of_noreturn_in_loop : $@convention(thin) () -> () {
Expand Down
4 changes: 1 addition & 3 deletions test/SILOptimizer/simplify_cfg_unique_values.sil
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Expand Up @@ -13,9 +13,7 @@ enum DupCaseEnum {
// CHECK-LABEL: sil @performSwitch : $@convention(thin) (Int64, @thin DupCaseEnum.Type) -> DupCaseEnum {
// CHECK: bb0(%0 : $Int64, %1 : $@thin DupCaseEnum.Type):
// CHECK: select_value
// CHECK: br bb1
// CHECK: bb1:
// CHECK: return
// CHECK-NEXT: return
sil @performSwitch : $@convention(thin) (Int64, @thin DupCaseEnum.Type) -> DupCaseEnum {
// %0 // users: %9, %5, %3, %2
bb0(%0 : $Int64, %1 : $@thin DupCaseEnum.Type):
Expand Down