[llvm] [InstCombine] Add more cases for simplifying `(icmp (and/or x, Mask), y)` (PR #85138)
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Tue Mar 19 09:52:36 PDT 2024
================
@@ -4189,82 +4191,133 @@ static bool isMaskOrZero(const Value *V, bool Not, const SimplifyQuery &Q,
static Value *foldICmpWithLowBitMaskedVal(ICmpInst::Predicate Pred, Value *Op0,
Value *Op1, const SimplifyQuery &Q,
InstCombiner &IC) {
- Value *X, *M;
- bool NeedsNot = false;
-
- auto CheckMask = [&](Value *V, bool Not) {
- if (ICmpInst::isSigned(Pred) && !match(V, m_ImmConstant()))
- return false;
- return isMaskOrZero(V, Not, Q);
- };
-
- if (match(Op0, m_c_And(m_Specific(Op1), m_Value(M))) &&
- CheckMask(M, /*Not*/ false)) {
- X = Op1;
- } else if (match(Op1, m_Zero()) && ICmpInst::isEquality(Pred) &&
- match(Op0, m_OneUse(m_And(m_Value(X), m_Value(M))))) {
- NeedsNot = true;
- if (IC.isFreeToInvert(X, X->hasOneUse()) && CheckMask(X, /*Not*/ true))
- std::swap(X, M);
- else if (!IC.isFreeToInvert(M, M->hasOneUse()) ||
- !CheckMask(M, /*Not*/ true))
- return nullptr;
- } else {
- return nullptr;
- }
ICmpInst::Predicate DstPred;
switch (Pred) {
case ICmpInst::Predicate::ICMP_EQ:
- // x & (-1 >> y) == x -> x u<= (-1 >> y)
+ // x & Mask == x
+ // x & ~Mask == 0
+ // ~x | Mask == -1
+ // -> x u<= Mask
+ // x & ~Mask == ~Mask
+ // -> ~Mask u<= x
DstPred = ICmpInst::Predicate::ICMP_ULE;
break;
case ICmpInst::Predicate::ICMP_NE:
- // x & (-1 >> y) != x -> x u> (-1 >> y)
+ // x & Mask != x
+ // x & ~Mask != 0
+ // ~x | Mask != -1
+ // -> x u> Mask
+ // x & ~Mask != ~Mask
+ // -> ~Mask u> x
DstPred = ICmpInst::Predicate::ICMP_UGT;
break;
case ICmpInst::Predicate::ICMP_ULT:
- // x & (-1 >> y) u< x -> x u> (-1 >> y)
- // x u> x & (-1 >> y) -> x u> (-1 >> y)
+ // x & Mask u< x
+ // -> x u> Mask
+ // x & ~Mask u< ~Mask
+ // -> ~Mask u> x
DstPred = ICmpInst::Predicate::ICMP_UGT;
break;
case ICmpInst::Predicate::ICMP_UGE:
- // x & (-1 >> y) u>= x -> x u<= (-1 >> y)
- // x u<= x & (-1 >> y) -> x u<= (-1 >> y)
+ // x & Mask u>= x
+ // -> x u<= Mask
+ // x & ~Mask u>= ~Mask
+ // -> ~Mask u<= x
DstPred = ICmpInst::Predicate::ICMP_ULE;
break;
case ICmpInst::Predicate::ICMP_SLT:
- // x & (-1 >> y) s< x -> x s> (-1 >> y)
- // x s> x & (-1 >> y) -> x s> (-1 >> y)
- if (!match(M, m_Constant())) // Can not do this fold with non-constant.
- return nullptr;
- if (!match(M, m_NonNegative())) // Must not have any -1 vector elements.
- return nullptr;
+ // x & Mask s< x [iff Mask s>= 0]
+ // -> x s> Mask
+ // x & ~Mask s< ~Mask [iff ~Mask != 0]
+ // -> ~Mask s> x
DstPred = ICmpInst::Predicate::ICMP_SGT;
break;
case ICmpInst::Predicate::ICMP_SGE:
- // x & (-1 >> y) s>= x -> x s<= (-1 >> y)
- // x s<= x & (-1 >> y) -> x s<= (-1 >> y)
- if (!match(M, m_Constant())) // Can not do this fold with non-constant.
- return nullptr;
- if (!match(M, m_NonNegative())) // Must not have any -1 vector elements.
- return nullptr;
+ // x & Mask s>= x [iff Mask s>= 0]
+ // -> x s<= Mask
+ // x & ~Mask s>= ~Mask [iff ~Mask != 0]
+ // -> ~Mask s<= x
DstPred = ICmpInst::Predicate::ICMP_SLE;
break;
- case ICmpInst::Predicate::ICMP_SGT:
- case ICmpInst::Predicate::ICMP_SLE:
- return nullptr;
- case ICmpInst::Predicate::ICMP_UGT:
- case ICmpInst::Predicate::ICMP_ULE:
- llvm_unreachable("Instsimplify took care of commut. variant");
- break;
default:
- llvm_unreachable("All possible folds are handled.");
+ // We don't support sgt,sle
+ // ult/ugt are simplified to true/false respectively.
+ return nullptr;
}
- // The mask value may be a vector constant that has undefined elements. But it
- // may not be safe to propagate those undefs into the new compare, so replace
- // those elements by copying an existing, defined, and safe scalar constant.
+ Value *X, *M;
+ // Put search code in lambda for early positive returns.
+ auto IsLowBitMask = [&]() {
+ if (match(Op0, m_c_And(m_Specific(Op1), m_Value(M)))) {
+ X = Op1;
+ // Look for: x & Mask pred x
+ if (isMaskOrZero(M, /*Not=*/false, Q)) {
+ return !ICmpInst::isSigned(Pred) ||
+ (match(M, m_NonNegative()) || isKnownNonNegative(M, Q));
+ }
+
+ // Look for: x & ~Mask pred ~Mask
+ if (isMaskOrZero(X, /*Not=*/true, Q)) {
+ return !ICmpInst::isSigned(Pred) ||
+ isKnownNonZero(X, Q.DL, /*Depth=*/0, Q.AC, Q.CxtI, Q.DT);
+ }
+ return false;
+ }
+ if (ICmpInst::isEquality(Pred) && match(Op1, m_AllOnes()) &&
+ match(Op0, m_OneUse(m_Or(m_Value(X), m_Value(M))))) {
+
+ auto Check = [&]() {
+ // Look for: ~x | Mask == -1
+ if (isMaskOrZero(M, /*Not=*/false, Q)) {
+ if (Value *NotX =
+ IC.getFreelyInverted(X, X->hasOneUse(), &IC.Builder)) {
+ X = NotX;
+ return true;
+ }
+ }
+ return false;
+ };
+ if (Check())
+ return true;
+ std::swap(X, M);
+
+ if (Check())
+ return true;
+
+ return false;
+ }
+ if (ICmpInst::isEquality(Pred) && match(Op1, m_Zero()) &&
+ match(Op0, m_OneUse(m_And(m_Value(X), m_Value(M))))) {
+ auto Check = [&]() {
+ // Look for: x & ~Mask == 0
+ if (isMaskOrZero(M, /*Not=*/true, Q)) {
+ if (Value *NotM =
+ IC.getFreelyInverted(M, M->hasOneUse(), &IC.Builder)) {
+ M = NotM;
+ return true;
+ }
+ }
+ return false;
+ };
+ if (Check())
+ return true;
+ std::swap(X, M);
+ if (Check())
+ return true;
+
+ return false;
----------------
nikic wrote:
```suggestion
return Check();
```
https://github.com/llvm/llvm-project/pull/85138
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