Jay Foad d7e03df719 [AMDGPU] Implement widening multiplies with v_mad_i64_i32/v_mad_u64_u32 ...

Select SelectionDAG ops smul_lohi/umul_lohi to
v_mad_i64_i32/v_mad_u64_u32 respectively, with an addend of 0.
v_mul_lo, v_mul_hi and v_mad_i64/u64 are all quarter-rate instructions
so it is better to use one instruction than two.

Further improvements are possible to make better use of the addend
operand, but this is already a strict improvement over what we have
now.

Differential Revision: https://reviews.llvm.org/D113986

2021-11-24 11:25:02 +00:00

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