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SimplifyCFG: Track the number of used icmps when turning a icmp chain into a switch. If we used only one icmp, don't turn it into a switch.

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Also prevent the switch-to-icmp transform from creating identity adds, noticed by Marius Wachtler.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125056 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2011-02-07 22:37:28 +00:00
parent 706d946cfe
commit 33828bcb24
4 changed files with 52 additions and 17 deletions
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29
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -305,7 +305,7 @@ static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
/// Values vector.
static Value *
GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
const TargetData *TD, bool isEQ) {
const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
Instruction *I = dyn_cast<Instruction>(V);
if (I == 0) return 0;
@ -313,6 +313,7 @@ GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
UsedICmps++;
Vals.push_back(C);
return I->getOperand(0);
}
@ -335,6 +336,7 @@ GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
UsedICmps++;
return I->getOperand(0);
}
return 0;
@ -345,14 +347,17 @@ GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
return 0;
unsigned NumValsBeforeLHS = Vals.size();
unsigned UsedICmpsBeforeLHS = UsedICmps;
if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
isEQ)) {
isEQ, UsedICmps)) {
unsigned NumVals = Vals.size();
unsigned UsedICmpsBeforeRHS = UsedICmps;
if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
isEQ)) {
isEQ, UsedICmps)) {
if (LHS == RHS)
return LHS;
Vals.resize(NumVals);
UsedICmps = UsedICmpsBeforeRHS;
}
// The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
@ -363,6 +368,7 @@ GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
}
Vals.resize(NumValsBeforeLHS);
UsedICmps = UsedICmpsBeforeLHS;
return 0;
}
@ -372,7 +378,7 @@ GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
Value *OldExtra = Extra;
Extra = I->getOperand(0);
if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
isEQ))
isEQ, UsedICmps))
return RHS;
assert(Vals.size() == NumValsBeforeLHS);
Extra = OldExtra;
@ -1926,17 +1932,24 @@ static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) {
std::vector<ConstantInt*> Values;
bool TrueWhenEqual = true;
Value *ExtraCase = 0;
unsigned UsedICmps = 0;
if (Cond->getOpcode() == Instruction::Or) {
CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true);
CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
UsedICmps);
} else if (Cond->getOpcode() == Instruction::And) {
CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false);
CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
UsedICmps);
TrueWhenEqual = false;
}
// If we didn't have a multiply compared value, fail.
if (CompVal == 0) return false;
// Avoid turning single icmps into a switch.
if (UsedICmps <= 1)
return false;
// There might be duplicate constants in the list, which the switch
// instruction can't handle, remove them now.
array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
@ -2262,7 +2275,9 @@ static bool TurnSwitchRangeIntoICmp(SwitchInst *SI) {
Constant *Offset = ConstantExpr::getNeg(Cases.back());
Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1);
Value *Sub = BinaryOperator::CreateAdd(SI->getCondition(), Offset, "off", SI);
Value *Sub = SI->getCondition();
if (!Offset->isNullValue())
Sub = BinaryOperator::CreateAdd(Sub, Offset, Sub->getName()+".off", SI);
Value *Cmp = new ICmpInst(SI, ICmpInst::ICMP_ULT, Sub, NumCases, "switch");
BranchInst::Create(SI->getSuccessor(1), SI->getDefaultDest(), Cmp, SI);

7
test/Transforms/SimplifyCFG/switch-to-icmp.ll
View File

@ -16,8 +16,8 @@ lor.end:
ret i1 %0
; CHECK: @test1
; CHECK: %off = add i32 %x, -1
; CHECK: %switch = icmp ult i32 %off, 3
; CHECK: %x.off = add i32 %x, -1
; CHECK: %switch = icmp ult i32 %x.off, 3
}
define zeroext i1 @test2(i32 %x) nounwind readnone ssp noredzone {
@ -35,6 +35,5 @@ lor.end:
ret i1 %0
; CHECK: @test2
; CHECK: %off = add i32 %x, 0
; CHECK: %switch = icmp ult i32 %off, 2
; CHECK: %switch = icmp ult i32 %x, 2
}

29
test/Transforms/SimplifyCFG/switch_create.ll
View File

@ -141,8 +141,8 @@ UnifiedReturnBlock: ; preds = %shortcirc_done.4, %shortcirc_next.4
ret i1 %UnifiedRetVal
; CHECK: @test6
; CHECK: %off = add i32 %tmp.2.i, -14
; CHECK: %switch = icmp ult i32 %off, 6
; CHECK: %tmp.2.i.off = add i32 %tmp.2.i, -14
; CHECK: %switch = icmp ult i32 %tmp.2.i.off, 6
}
define void @test7(i8 zeroext %c, i32 %x) nounwind ssp noredzone {
@ -441,8 +441,8 @@ if.end:
define zeroext i1 @test16(i32 %x) nounwind {
entry:
; CHECK: @test16
; CHECK: %off = add i32 %x, -1
; CHECK: %switch = icmp ult i32 %off, 3
; CHECK: %x.off = add i32 %x, -1
; CHECK: %switch = icmp ult i32 %x.off, 3
%cmp.i = icmp eq i32 %x, 1
br i1 %cmp.i, label %lor.end, label %lor.lhs.false
@ -458,3 +458,24 @@ lor.end:
%0 = phi i1 [ true, %lor.lhs.false ], [ true, %entry ], [ %cmp.i1, %lor.rhs ]
ret i1 %0
}
; Check that we don't turn an icmp into a switch where it's not useful.
define void @test17(i32 %x, i32 %y) {
%cmp = icmp ult i32 %x, 3
%switch = icmp ult i32 %y, 2
%or.cond775 = or i1 %cmp, %switch
br i1 %or.cond775, label %lor.lhs.false8, label %return
lor.lhs.false8:
tail call void @foo1()
ret void
return:
ret void
; CHECK: @test17
; CHECK-NOT: switch.early.test
; CHECK-NOT: switch i32
; CHECK: ret void
}

4
test/Transforms/SimplifyCFG/switch_formation.dbg.ll
View File

@ -14,8 +14,8 @@ declare void @llvm.dbg.stoppoint(i32, i32, { }*) nounwind
define i1 @t({ i32, i32 }* %I) {
; CHECK: @t
; CHECK: %off = add i32 %tmp.2.i, -14
; CHECK: %switch = icmp ult i32 %off, 6
; CHECK: %tmp.2.i.off = add i32 %tmp.2.i, -14
; CHECK: %switch = icmp ult i32 %tmp.2.i.off, 6
entry:
%tmp.1.i = getelementptr { i32, i32 }* %I, i64 0, i32 1 ; <i32*> [#uses=1]
%tmp.2.i = load i32* %tmp.1.i ; <i32> [#uses=6]