[Bug inline-asm/36048] wrong assumption about registers used in asm statements

[jlima at sim dot ul dot pt]

------- Comment #2 from jlima at sim dot ul dot pt  2008-04-25 20:56 -------
If this is the expected behavior... then ok.
I saw this as a bug because it is not possible to add the register to the
clobbered registers list (gcc will complain with: "error: can't find a register
in class 'DREG' while reloading 'asm'") and it is not elegant to define the
register as an output register when the result is to be disregarded. Even if
the optimizing compiler can detect that and suppress the unused code.

It often required to modify/reuse an input register inside the inline assembly
statement. In such cases, if I understood well, one must restore the register
to its original value if optimization is to be used. But this may imply a
suboptimal code since it will always be restored regardless of being required
or not.



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36048