Vikash Gupta 0b0d9a3bee [CodeGen] [AMDGPU] Attempt DAGCombine for fmul with select to ldexp (#111109) ...

The materialization cost of 32-bit non-inline in case of fmul is quite
relatively more, rather than if possible to combine it into ldexp
instruction for specific scenarios (for datatypes like f64, f32 and f16)
as this is being handled here :

The dag combine for any pair of select values which are exact exponent
of 2.

```
fmul x, select(y, A, B)       -> ldexp (x, select i32 (y, a, b))
fmul x, select(y, -A, -B)    -> ldexp ((fneg x), select i32 (y, a, b))

where, A=2^a & B=2^b ; a and b are integers.  
```

This dagCombine is handled separately in fmulCombine (newly defined in
SIIselLowering), targeting fmul fusing it with select type operand into
ldexp.

Thus, it fixes #104900.

2024-12-09 12:52:04 +05:30

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