[InstCombine] X | C == C --> (X & ~C) == 0
We should canonicalize to one of these forms,
and compare-with-zero could be more conducive
to follow-on transforms. This also leads to
generally better codegen as shown in PR40611:
https://bugs.llvm.org/show_bug.cgi?id=40611
llvm-svn: 353313
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index ba03dcb..399aa2d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1771,13 +1771,22 @@
ConstantInt::get(V->getType(), 1));
}
- // X | C == C --> X <=u C
- // X | C != C --> X >u C
- // iff C+1 is a power of 2 (C is a bitmask of the low bits)
- if (Cmp.isEquality() && Cmp.getOperand(1) == Or->getOperand(1) &&
- (C + 1).isPowerOf2()) {
- Pred = (Pred == CmpInst::ICMP_EQ) ? CmpInst::ICMP_ULE : CmpInst::ICMP_UGT;
- return new ICmpInst(Pred, Or->getOperand(0), Or->getOperand(1));
+ Value *OrOp0 = Or->getOperand(0), *OrOp1 = Or->getOperand(1);
+ if (Cmp.isEquality() && Cmp.getOperand(1) == OrOp1) {
+ // X | C == C --> X <=u C
+ // X | C != C --> X >u C
+ // iff C+1 is a power of 2 (C is a bitmask of the low bits)
+ if ((C + 1).isPowerOf2()) {
+ Pred = (Pred == CmpInst::ICMP_EQ) ? CmpInst::ICMP_ULE : CmpInst::ICMP_UGT;
+ return new ICmpInst(Pred, OrOp0, OrOp1);
+ }
+ // More general: are all bits outside of a mask constant set or not set?
+ // X | C == C --> (X & ~C) == 0
+ // X | C != C --> (X & ~C) != 0
+ if (Or->hasOneUse()) {
+ Value *A = Builder.CreateAnd(OrOp0, ~C);
+ return new ICmpInst(Pred, A, ConstantInt::getNullValue(OrOp0->getType()));
+ }
}
if (!Cmp.isEquality() || !C.isNullValue() || !Or->hasOneUse())
@@ -1798,8 +1807,8 @@
// Are we using xors to bitwise check for a pair of (in)equalities? Convert to
// a shorter form that has more potential to be folded even further.
Value *X1, *X2, *X3, *X4;
- if (match(Or->getOperand(0), m_OneUse(m_Xor(m_Value(X1), m_Value(X2)))) &&
- match(Or->getOperand(1), m_OneUse(m_Xor(m_Value(X3), m_Value(X4))))) {
+ if (match(OrOp0, m_OneUse(m_Xor(m_Value(X1), m_Value(X2)))) &&
+ match(OrOp1, m_OneUse(m_Xor(m_Value(X3), m_Value(X4))))) {
// ((X1 ^ X2) || (X3 ^ X4)) == 0 --> (X1 == X2) && (X3 == X4)
// ((X1 ^ X2) || (X3 ^ X4)) != 0 --> (X1 != X2) || (X3 != X4)
Value *Cmp12 = Builder.CreateICmp(Pred, X1, X2);