[PATCH] Fix asm X constraint (PR inline-asm/59155)

[Bernd Edlinger]

Hi!

This restricts the X constraint in asm statements, which
can be easily folded by combine in something completely
invalid.

It is necessary to allow scratch here, because on i386
the md_asm_adjust hook inserts them.

The second test case fails because lra does not
allow all register for anything_ok operands (aka X)
and later it fails to match the two X constraints
in case '0': if (curr_alt[m] == NO_REGS) break.

There is also an identical bug in the reload pass,
but I do not know how to fix that, as it is almost
used nowhere today.


Boot-strapped and regression-tested on x86_64-pc-linux-gnu.
OK for trunk?


Thanks
Bernd.
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