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
diff --git a/llvm/lib/Transforms/InstCombine/InstCombine.h b/llvm/lib/Transforms/InstCombine/InstCombine.h
index 3e53b73..05ce02a92 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombine.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombine.h
@@ -162,6 +162,7 @@
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);
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 60b859f..c1d04f7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -785,6 +785,63 @@
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 @@
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 @@
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;