+/// SimplifyICmpOperands - Simplify LHS and RHS in a comparison with
+/// predicate Pred. Return true iff any changes were made.
+///
+bool ScalarEvolution::SimplifyICmpOperands(ICmpInst::Predicate &Pred,
+ const SCEV *&LHS, const SCEV *&RHS) {
+ bool Changed = false;
+
+ // Canonicalize a constant to the right side.
+ if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(LHS)) {
+ // Check for both operands constant.
+ if (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS)) {
+ if (ConstantExpr::getICmp(Pred,
+ LHSC->getValue(),
+ RHSC->getValue())->isNullValue())
+ goto trivially_false;
+ else
+ goto trivially_true;
+ }
+ // Otherwise swap the operands to put the constant on the right.
+ std::swap(LHS, RHS);
+ Pred = ICmpInst::getSwappedPredicate(Pred);
+ Changed = true;
+ }
+
+ // If we're comparing an addrec with a value which is loop-invariant in the
+ // addrec's loop, put the addrec on the left. Also make a dominance check,
+ // as both operands could be addrecs loop-invariant in each other's loop.
+ if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(RHS)) {
+ const Loop *L = AR->getLoop();
+ if (LHS->isLoopInvariant(L) && LHS->properlyDominates(L->getHeader(), DT)) {
+ std::swap(LHS, RHS);
+ Pred = ICmpInst::getSwappedPredicate(Pred);
+ Changed = true;
+ }
+ }
+
+ // If there's a constant operand, canonicalize comparisons with boundary
+ // cases, and canonicalize *-or-equal comparisons to regular comparisons.
+ if (const SCEVConstant *RC = dyn_cast<SCEVConstant>(RHS)) {
+ const APInt &RA = RC->getValue()->getValue();
+ switch (Pred) {
+ default: llvm_unreachable("Unexpected ICmpInst::Predicate value!");
+ case ICmpInst::ICMP_EQ:
+ case ICmpInst::ICMP_NE:
+ break;
+ case ICmpInst::ICMP_UGE:
+ if ((RA - 1).isMinValue()) {
+ Pred = ICmpInst::ICMP_NE;
+ RHS = getConstant(RA - 1);
+ Changed = true;
+ break;
+ }
+ if (RA.isMaxValue()) {
+ Pred = ICmpInst::ICMP_EQ;
+ Changed = true;
+ break;
+ }
+ if (RA.isMinValue()) goto trivially_true;
+
+ Pred = ICmpInst::ICMP_UGT;
+ RHS = getConstant(RA - 1);
+ Changed = true;
+ break;
+ case ICmpInst::ICMP_ULE:
+ if ((RA + 1).isMaxValue()) {
+ Pred = ICmpInst::ICMP_NE;
+ RHS = getConstant(RA + 1);
+ Changed = true;
+ break;
+ }
+ if (RA.isMinValue()) {
+ Pred = ICmpInst::ICMP_EQ;
+ Changed = true;
+ break;
+ }
+ if (RA.isMaxValue()) goto trivially_true;
+
+ Pred = ICmpInst::ICMP_ULT;
+ RHS = getConstant(RA + 1);
+ Changed = true;
+ break;
+ case ICmpInst::ICMP_SGE:
+ if ((RA - 1).isMinSignedValue()) {
+ Pred = ICmpInst::ICMP_NE;
+ RHS = getConstant(RA - 1);
+ Changed = true;
+ break;
+ }
+ if (RA.isMaxSignedValue()) {
+ Pred = ICmpInst::ICMP_EQ;
+ Changed = true;
+ break;
+ }
+ if (RA.isMinSignedValue()) goto trivially_true;
+
+ Pred = ICmpInst::ICMP_SGT;
+ RHS = getConstant(RA - 1);
+ Changed = true;
+ break;
+ case ICmpInst::ICMP_SLE:
+ if ((RA + 1).isMaxSignedValue()) {
+ Pred = ICmpInst::ICMP_NE;
+ RHS = getConstant(RA + 1);
+ Changed = true;
+ break;
+ }
+ if (RA.isMinSignedValue()) {
+ Pred = ICmpInst::ICMP_EQ;
+ Changed = true;
+ break;
+ }
+ if (RA.isMaxSignedValue()) goto trivially_true;
+
+ Pred = ICmpInst::ICMP_SLT;
+ RHS = getConstant(RA + 1);
+ Changed = true;
+ break;
+ case ICmpInst::ICMP_UGT:
+ if (RA.isMinValue()) {
+ Pred = ICmpInst::ICMP_NE;
+ Changed = true;
+ break;
+ }
+ if ((RA + 1).isMaxValue()) {
+ Pred = ICmpInst::ICMP_EQ;
+ RHS = getConstant(RA + 1);
+ Changed = true;
+ break;
+ }
+ if (RA.isMaxValue()) goto trivially_false;
+ break;
+ case ICmpInst::ICMP_ULT:
+ if (RA.isMaxValue()) {
+ Pred = ICmpInst::ICMP_NE;
+ Changed = true;
+ break;
+ }
+ if ((RA - 1).isMinValue()) {
+ Pred = ICmpInst::ICMP_EQ;
+ RHS = getConstant(RA - 1);
+ Changed = true;
+ break;
+ }
+ if (RA.isMinValue()) goto trivially_false;
+ break;
+ case ICmpInst::ICMP_SGT:
+ if (RA.isMinSignedValue()) {
+ Pred = ICmpInst::ICMP_NE;
+ Changed = true;
+ break;
+ }
+ if ((RA + 1).isMaxSignedValue()) {
+ Pred = ICmpInst::ICMP_EQ;
+ RHS = getConstant(RA + 1);
+ Changed = true;
+ break;
+ }
+ if (RA.isMaxSignedValue()) goto trivially_false;
+ break;
+ case ICmpInst::ICMP_SLT:
+ if (RA.isMaxSignedValue()) {
+ Pred = ICmpInst::ICMP_NE;
+ Changed = true;
+ break;
+ }
+ if ((RA - 1).isMinSignedValue()) {
+ Pred = ICmpInst::ICMP_EQ;
+ RHS = getConstant(RA - 1);
+ Changed = true;
+ break;
+ }
+ if (RA.isMinSignedValue()) goto trivially_false;
+ break;
+ }
+ }
+
+ // Check for obvious equality.
+ if (HasSameValue(LHS, RHS)) {
+ if (ICmpInst::isTrueWhenEqual(Pred))
+ goto trivially_true;
+ if (ICmpInst::isFalseWhenEqual(Pred))
+ goto trivially_false;
+ }
+
+ // If possible, canonicalize GE/LE comparisons to GT/LT comparisons, by
+ // adding or subtracting 1 from one of the operands.
+ switch (Pred) {
+ case ICmpInst::ICMP_SLE:
+ if (!getSignedRange(RHS).getSignedMax().isMaxSignedValue()) {
+ RHS = getAddExpr(getConstant(RHS->getType(), 1, true), RHS,
+ /*HasNUW=*/false, /*HasNSW=*/true);
+ Pred = ICmpInst::ICMP_SLT;
+ Changed = true;
+ } else if (!getSignedRange(LHS).getSignedMin().isMinSignedValue()) {
+ LHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), LHS,
+ /*HasNUW=*/false, /*HasNSW=*/true);
+ Pred = ICmpInst::ICMP_SLT;
+ Changed = true;
+ }
+ break;
+ case ICmpInst::ICMP_SGE:
+ if (!getSignedRange(RHS).getSignedMin().isMinSignedValue()) {
+ RHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), RHS,
+ /*HasNUW=*/false, /*HasNSW=*/true);
+ Pred = ICmpInst::ICMP_SGT;
+ Changed = true;
+ } else if (!getSignedRange(LHS).getSignedMax().isMaxSignedValue()) {
+ LHS = getAddExpr(getConstant(RHS->getType(), 1, true), LHS,
+ /*HasNUW=*/false, /*HasNSW=*/true);
+ Pred = ICmpInst::ICMP_SGT;
+ Changed = true;
+ }
+ break;
+ case ICmpInst::ICMP_ULE:
+ if (!getUnsignedRange(RHS).getUnsignedMax().isMaxValue()) {
+ RHS = getAddExpr(getConstant(RHS->getType(), 1, true), RHS,
+ /*HasNUW=*/true, /*HasNSW=*/false);
+ Pred = ICmpInst::ICMP_ULT;
+ Changed = true;
+ } else if (!getUnsignedRange(LHS).getUnsignedMin().isMinValue()) {
+ LHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), LHS,
+ /*HasNUW=*/true, /*HasNSW=*/false);
+ Pred = ICmpInst::ICMP_ULT;
+ Changed = true;
+ }
+ break;
+ case ICmpInst::ICMP_UGE:
+ if (!getUnsignedRange(RHS).getUnsignedMin().isMinValue()) {
+ RHS = getAddExpr(getConstant(RHS->getType(), (uint64_t)-1, true), RHS,
+ /*HasNUW=*/true, /*HasNSW=*/false);
+ Pred = ICmpInst::ICMP_UGT;
+ Changed = true;
+ } else if (!getUnsignedRange(LHS).getUnsignedMax().isMaxValue()) {
+ LHS = getAddExpr(getConstant(RHS->getType(), 1, true), LHS,
+ /*HasNUW=*/true, /*HasNSW=*/false);
+ Pred = ICmpInst::ICMP_UGT;
+ Changed = true;
+ }
+ break;
+ default:
+ break;
+ }
+
+ // TODO: More simplifications are possible here.
+
+ return Changed;
+
+trivially_true:
+ // Return 0 == 0.
+ LHS = RHS = getConstant(Type::getInt1Ty(getContext()), 0);
+ Pred = ICmpInst::ICMP_EQ;
+ return true;
+
+trivially_false:
+ // Return 0 != 0.
+ LHS = RHS = getConstant(Type::getInt1Ty(getContext()), 0);
+ Pred = ICmpInst::ICMP_NE;
+ return true;
+}
+