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Re: [patch, tree-ssa] PR54295 Incorrect value extension in widening multiply-accumulate

On 17/08/12 16:20, Richard Earnshaw wrote: 
No, given a u16xu16->u64 operation in the code, and that the arch
doesn't have such an opcode, I'd expect to get

step1 -> (u32)u16 x (u32)u16 -> u64

Hmm, I would have thought that would be more costly than

(u64)(u16 x u16 -> u32)

You might be right, but then extends are often free, especially with unsigned types, so it's hard to say for sure.

Did you reproduce one? It's a long time since I last looked at this stuff, so I could be confused.

Andrew

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