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Re: regrename creates invalid insn

Andreas Schwab <> writes:

> When regrename runs it turns it into this:
> (insn 6 27 7 2 (parallel [
>             (set (reg:SI 1 %d1 [35])
>                 (truncate:SI (lshiftrt:DI (mult:DI (sign_extend:DI (reg:SI 1 %d1 [36]))
>                             (const_int -2004318071 [0x88888889]))
>                         (const_int 32 [0x20]))))
>             (clobber (reg:SI 1 %d1 [36]))
>         ]) mulsl.c:4 192 {const_smulsi3_highpart}
>      (expr_list:REG_UNUSED (reg:SI 1 %d1 [36])
>         (nil)))
> Note that both output operands are allocated to the same register (which
> generates a muls.l producing undefined results).  Is this transformation
> actually valid?  I can stop regrename from doing this by marking operand
> 0 as earlyclobber, but the insn doesn't actually write the outputs
> before reading the inputs, the issue is the dependency between the
> outputs.

I assume there were two different hard register numbers before
regrename.  That does not look like a valid transformation to me.

But it also looks like the pattern should use a match_scratch.


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