InstCombine: simplify signed range checks

Try to convert two compares of a signed range check into a single unsigned compare.
Examples:
(icmp sge x, 0) & (icmp slt x, n) --> icmp ult x, n
(icmp slt x, 0) | (icmp sgt x, n) --> icmp ugt x, n

llvm-svn: 223224
This commit is contained in:
Erik Eckstein 2014-12-03 10:39:15 +00:00
parent 25383ac01b
commit d181752be0
3 changed files with 233 additions and 0 deletions

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@ -162,6 +162,7 @@ public:
Instruction *visitUDiv(BinaryOperator &I);
Instruction *visitSDiv(BinaryOperator &I);
Instruction *visitFDiv(BinaryOperator &I);
Value *simplifyRangeCheck(ICmpInst *Cmp0, ICmpInst *Cmp1, bool Inverted);
Value *FoldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS);
Value *FoldAndOfFCmps(FCmpInst *LHS, FCmpInst *RHS);
Instruction *visitAnd(BinaryOperator &I);

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@ -785,6 +785,63 @@ static Value *foldLogOpOfMaskedICmps(ICmpInst *LHS, ICmpInst *RHS, bool IsAnd,
return nullptr;
}
/// Try to fold a signed range checked with lower bound 0 to an unsigned icmp.
/// Example: (icmp sge x, 0) & (icmp slt x, n) --> icmp ult x, n
/// If \p Inverted is true then the check is for the inverted range, e.g.
/// (icmp slt x, 0) | (icmp sgt x, n) --> icmp ugt x, n
Value *InstCombiner::simplifyRangeCheck(ICmpInst *Cmp0, ICmpInst *Cmp1,
bool Inverted) {
// Check the lower range comparison, e.g. x >= 0
// InstCombine already ensured that if there is a constant it's on the RHS.
ConstantInt *RangeStart = dyn_cast<ConstantInt>(Cmp0->getOperand(1));
if (!RangeStart)
return nullptr;
ICmpInst::Predicate Pred0 = (Inverted ? Cmp0->getInversePredicate() :
Cmp0->getPredicate());
// Accept x > -1 or x >= 0 (after potentially inverting the predicate).
if (!((Pred0 == ICmpInst::ICMP_SGT && RangeStart->isMinusOne()) ||
(Pred0 == ICmpInst::ICMP_SGE && RangeStart->isZero())))
return nullptr;
ICmpInst::Predicate Pred1 = (Inverted ? Cmp1->getInversePredicate() :
Cmp1->getPredicate());
Value *Input = Cmp0->getOperand(0);
Value *RangeEnd;
if (Cmp1->getOperand(0) == Input) {
// For the upper range compare we have: icmp x, n
RangeEnd = Cmp1->getOperand(1);
} else if (Cmp1->getOperand(1) == Input) {
// For the upper range compare we have: icmp n, x
RangeEnd = Cmp1->getOperand(0);
Pred1 = ICmpInst::getSwappedPredicate(Pred1);
} else {
return nullptr;
}
// Check the upper range comparison, e.g. x < n
ICmpInst::Predicate NewPred;
switch (Pred1) {
case ICmpInst::ICMP_SLT: NewPred = ICmpInst::ICMP_ULT; break;
case ICmpInst::ICMP_SLE: NewPred = ICmpInst::ICMP_ULE; break;
default: return nullptr;
}
// This simplification is only valid if the upper range is not negative.
bool IsNegative, IsNotNegative;
ComputeSignBit(RangeEnd, IsNotNegative, IsNegative, DL, 0, AT,
Cmp1, DT);
if (!IsNotNegative)
return nullptr;
if (Inverted)
NewPred = ICmpInst::getInversePredicate(NewPred);
return Builder->CreateICmp(NewPred, Input, RangeEnd);
}
/// FoldAndOfICmps - Fold (icmp)&(icmp) if possible.
Value *InstCombiner::FoldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
ICmpInst::Predicate LHSCC = LHS->getPredicate(), RHSCC = RHS->getPredicate();
@ -807,6 +864,14 @@ Value *InstCombiner::FoldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
if (Value *V = foldLogOpOfMaskedICmps(LHS, RHS, true, Builder))
return V;
// E.g. (icmp sge x, 0) & (icmp slt x, n) --> icmp ult x, n
if (Value *V = simplifyRangeCheck(LHS, RHS, /*Inverted=*/false))
return V;
// E.g. (icmp slt x, n) & (icmp sge x, 0) --> icmp ult x, n
if (Value *V = simplifyRangeCheck(RHS, LHS, /*Inverted=*/false))
return V;
// This only handles icmp of constants: (icmp1 A, C1) & (icmp2 B, C2).
Value *Val = LHS->getOperand(0), *Val2 = RHS->getOperand(0);
ConstantInt *LHSCst = dyn_cast<ConstantInt>(LHS->getOperand(1));
@ -1724,6 +1789,14 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS,
Builder->CreateAdd(B, ConstantInt::getSigned(B->getType(), -1)), A);
}
// E.g. (icmp slt x, 0) | (icmp sgt x, n) --> icmp ugt x, n
if (Value *V = simplifyRangeCheck(LHS, RHS, /*Inverted=*/true))
return V;
// E.g. (icmp sgt x, n) | (icmp slt x, 0) --> icmp ugt x, n
if (Value *V = simplifyRangeCheck(RHS, LHS, /*Inverted=*/true))
return V;
// This only handles icmp of constants: (icmp1 A, C1) | (icmp2 B, C2).
if (!LHSCst || !RHSCst) return nullptr;

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@ -0,0 +1,159 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
; Check simplification of
; (icmp sgt x, -1) & (icmp sgt/sge n, x) --> icmp ugt/uge n, x
; CHECK-LABEL: define i1 @test_and1
; CHECK: [[R:%[0-9]+]] = icmp ugt i32 %nn, %x
; CHECK: ret i1 [[R]]
define i1 @test_and1(i32 %x, i32 %n) {
%nn = and i32 %n, 2147483647
%a = icmp sge i32 %x, 0
%b = icmp slt i32 %x, %nn
%c = and i1 %a, %b
ret i1 %c
}
; CHECK-LABEL: define i1 @test_and2
; CHECK: [[R:%[0-9]+]] = icmp uge i32 %nn, %x
; CHECK: ret i1 [[R]]
define i1 @test_and2(i32 %x, i32 %n) {
%nn = and i32 %n, 2147483647
%a = icmp sgt i32 %x, -1
%b = icmp sle i32 %x, %nn
%c = and i1 %a, %b
ret i1 %c
}
; CHECK-LABEL: define i1 @test_and3
; CHECK: [[R:%[0-9]+]] = icmp ugt i32 %nn, %x
; CHECK: ret i1 [[R]]
define i1 @test_and3(i32 %x, i32 %n) {
%nn = and i32 %n, 2147483647
%a = icmp sgt i32 %nn, %x
%b = icmp sge i32 %x, 0
%c = and i1 %a, %b
ret i1 %c
}
; CHECK-LABEL: define i1 @test_and4
; CHECK: [[R:%[0-9]+]] = icmp uge i32 %nn, %x
; CHECK: ret i1 [[R]]
define i1 @test_and4(i32 %x, i32 %n) {
%nn = and i32 %n, 2147483647
%a = icmp sge i32 %nn, %x
%b = icmp sge i32 %x, 0
%c = and i1 %a, %b
ret i1 %c
}
; CHECK-LABEL: define i1 @test_or1
; CHECK: [[R:%[0-9]+]] = icmp ule i32 %nn, %x
; CHECK: ret i1 [[R]]
define i1 @test_or1(i32 %x, i32 %n) {
%nn = and i32 %n, 2147483647
%a = icmp slt i32 %x, 0
%b = icmp sge i32 %x, %nn
%c = or i1 %a, %b
ret i1 %c
}
; CHECK-LABEL: define i1 @test_or2
; CHECK: [[R:%[0-9]+]] = icmp ult i32 %nn, %x
; CHECK: ret i1 [[R]]
define i1 @test_or2(i32 %x, i32 %n) {
%nn = and i32 %n, 2147483647
%a = icmp sle i32 %x, -1
%b = icmp sgt i32 %x, %nn
%c = or i1 %a, %b
ret i1 %c
}
; CHECK-LABEL: define i1 @test_or3
; CHECK: [[R:%[0-9]+]] = icmp ule i32 %nn, %x
; CHECK: ret i1 [[R]]
define i1 @test_or3(i32 %x, i32 %n) {
%nn = and i32 %n, 2147483647
%a = icmp sle i32 %nn, %x
%b = icmp slt i32 %x, 0
%c = or i1 %a, %b
ret i1 %c
}
; CHECK-LABEL: define i1 @test_or4
; CHECK: [[R:%[0-9]+]] = icmp ult i32 %nn, %x
; CHECK: ret i1 [[R]]
define i1 @test_or4(i32 %x, i32 %n) {
%nn = and i32 %n, 2147483647
%a = icmp slt i32 %nn, %x
%b = icmp slt i32 %x, 0
%c = or i1 %a, %b
ret i1 %c
}
; Negative tests
; CHECK-LABEL: define i1 @negative1
; CHECK: %a = icmp
; CHECK: %b = icmp
; CHECK: %c = and i1 %a, %b
; CHECK: ret i1 %c
define i1 @negative1(i32 %x, i32 %n) {
%nn = and i32 %n, 2147483647
%a = icmp slt i32 %x, %nn
%b = icmp sgt i32 %x, 0 ; should be: icmp sge
%c = and i1 %a, %b
ret i1 %c
}
; CHECK-LABEL: define i1 @negative2
; CHECK: %a = icmp
; CHECK: %b = icmp
; CHECK: %c = and i1 %a, %b
; CHECK: ret i1 %c
define i1 @negative2(i32 %x, i32 %n) {
%a = icmp slt i32 %x, %n ; n can be negative
%b = icmp sge i32 %x, 0
%c = and i1 %a, %b
ret i1 %c
}
; CHECK-LABEL: define i1 @negative3
; CHECK: %a = icmp
; CHECK: %b = icmp
; CHECK: %c = and i1 %a, %b
; CHECK: ret i1 %c
define i1 @negative3(i32 %x, i32 %y, i32 %n) {
%nn = and i32 %n, 2147483647
%a = icmp slt i32 %x, %nn
%b = icmp sge i32 %y, 0 ; should compare %x and not %y
%c = and i1 %a, %b
ret i1 %c
}
; CHECK-LABEL: define i1 @negative4
; CHECK: %a = icmp
; CHECK: %b = icmp
; CHECK: %c = and i1 %a, %b
; CHECK: ret i1 %c
define i1 @negative4(i32 %x, i32 %n) {
%nn = and i32 %n, 2147483647
%a = icmp ne i32 %x, %nn ; should be: icmp slt/sle
%b = icmp sge i32 %x, 0
%c = and i1 %a, %b
ret i1 %c
}
; CHECK-LABEL: define i1 @negative5
; CHECK: %a = icmp
; CHECK: %b = icmp
; CHECK: %c = or i1 %a, %b
; CHECK: ret i1 %c
define i1 @negative5(i32 %x, i32 %n) {
%nn = and i32 %n, 2147483647
%a = icmp slt i32 %x, %nn
%b = icmp sge i32 %x, 0
%c = or i1 %a, %b ; should be: and
ret i1 %c
}