[MLIR] Add f6E3M2FN type (#105573)

This PR adds `f6E3M2FN` type to mlir.

`f6E3M2FN` type is proposed in [OpenCompute MX
Specification](https://www.opencompute.org/documents/ocp-microscaling-formats-mx-v1-0-spec-final-pdf).
It defines a 6-bit floating point number with bit layout S1E3M2. Unlike
IEEE-754 types, there are no infinity or NaN values.

```c
f6E3M2FN
- Exponent bias: 3
- Maximum stored exponent value: 7 (binary 111)
- Maximum unbiased exponent value: 7 - 3 = 4
- Minimum stored exponent value: 1 (binary 001)
- Minimum unbiased exponent value: 1 − 3 = −2
- Has Positive and Negative zero
- Doesn't have infinity
- Doesn't have NaNs

Additional details:
- Zeros (+/-): S.000.00
- Max normal number: S.111.11 = ±2^(4) x (1 + 0.75) = ±28
- Min normal number: S.001.00 = ±2^(-2) = ±0.25
- Max subnormal number: S.000.11 = ±2^(-2) x 0.75 = ±0.1875
- Min subnormal number: S.000.01 = ±2^(-2) x 0.25 = ±0.0625
```

Related PRs:
- [PR-94735](https://github.com/llvm/llvm-project/pull/94735) [APFloat]
Add APFloat support for FP6 data types
- [PR-97118](https://github.com/llvm/llvm-project/pull/97118) [MLIR] Add
f8E4M3 type - was used as a template for this PR

1 files changed, 4 insertions, 3 deletions

diff --git a/llvm/unittests/ADT/APFloatTest.cpp b/llvm/unittests/ADT/APFloatTest.cpp
index be675bb..6c49d78e 100644
--- a/llvm/unittests/ADT/APFloatTest.cpp
+++ b/llvm/unittests/ADT/APFloatTest.cpp
@@ -2084,16 +2084,17 @@ TEST(APFloatTest, getSmallestNormalized) {
   EXPECT_FALSE(test.isDenormal());
   EXPECT_TRUE(test.bitwiseIsEqual(expected));
   EXPECT_TRUE(test.isSmallestNormalized());
+
   test = APFloat::getSmallestNormalized(APFloat::Float6E3M2FN(), false);
   expected = APFloat(APFloat::Float6E3M2FN(), "0x1p-2");
-
-  test = APFloat::getSmallestNormalized(APFloat::Float4E2M1FN(), false);
-  expected = APFloat(APFloat::Float4E2M1FN(), "0x1p0");
   EXPECT_FALSE(test.isNegative());
   EXPECT_TRUE(test.isFiniteNonZero());
   EXPECT_FALSE(test.isDenormal());
   EXPECT_TRUE(test.bitwiseIsEqual(expected));
   EXPECT_TRUE(test.isSmallestNormalized());
+
+  test = APFloat::getSmallestNormalized(APFloat::Float4E2M1FN(), false);
+  expected = APFloat(APFloat::Float4E2M1FN(), "0x1p0");
   EXPECT_FALSE(test.isNegative());
   EXPECT_TRUE(test.isFiniteNonZero());
   EXPECT_FALSE(test.isDenormal());