[SelectionDAG] Flags are dropped when creating a new FMUL #66701
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While simplifying some vector operators in DAG combine, we may need to create new instructions for simplified vectors. At that time, we need to make sure that all the flags of the new instruction are copied/modified from the old instruction. Here's an example where "contract" flag is dropped when FMUL is createted. Replacing.2 t42: v2f32 = fmul contract t41, t38 With: t48: v2f32 = fmul t38, t38
jayfoad
reviewed
Sep 19, 2023
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While simplifying some vector operators in DAG combine, we may need to create new instructions for simplified vectors. At that time, we need to make sure that all the flags of the new instruction are copied/modified from the old instruction.
If "contract" is dropped from an instruction like FMUL, it may not generate FMA instruction which would impact performance.
Here's an example where "contract" flag is dropped when FMUL is created.
Replacing.2 t42: v2f32 = fmul contract t41, t38
With: t48: v2f32 = fmul t38, t38