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[KnownBits] Check that mul is optimal for low order bits #113316

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Merged
jayfoad merged 1 commit into from
Oct 22, 2024
Merged

[KnownBits] Check that mul is optimal for low order bits #113316

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34 changes: 34 additions & 0 deletions llvm/unittests/Support/KnownBitsTest.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -815,4 +815,38 @@ TEST(KnownBitsTest, ConcatBits) {
}
}

TEST(KnownBitsTest, MulExhaustive) {
for (unsigned Bits : {1, 4}) {
ForeachKnownBits(Bits, [&](const KnownBits &Known1) {
ForeachKnownBits(Bits, [&](const KnownBits &Known2) {
KnownBits Computed = KnownBits::mul(Known1, Known2);
KnownBits Exact(Bits);
Exact.Zero.setAllBits();
Exact.One.setAllBits();

ForeachNumInKnownBits(Known1, [&](const APInt &N1) {
ForeachNumInKnownBits(Known2, [&](const APInt &N2) {
APInt Res = N1 * N2;
Exact.One &= Res;
Exact.Zero &= ~Res;
});
});

if (!Exact.hasConflict()) {
// Check that the result is optimal for the contiguous known low order
// bits.
APInt Mask = APInt::getLowBitsSet(
Bits, (Exact.Zero | Exact.One).countTrailingOnes());
Exact.Zero &= Mask;
Exact.One &= Mask;
Computed.Zero &= Mask;
Computed.One &= Mask;
EXPECT_TRUE(checkResult("mul", Exact, Computed, {Known1, Known2},
/*CheckOptimality=*/true));
}
});
});
}
}

} // end anonymous namespace
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