[Bug rtl-optimization/40667] [4.4/4.5 Regression] stack frames are generated even with -fomit-frame-pointer

["hjl dot tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #9 from hjl dot tools at gmail dot com  2009-07-09 13:57 -------
(In reply to comment #8)
> on -m32 we ever decrease the stack alignment, this shouldn't break anything.
> BTW, the patch also changes something that looks like a thinko to me:
>           unsigned int align = FUNCTION_ARG_BOUNDARY (data.promoted_mode,
>                                                       data.passed_type);
>           if (TYPE_ALIGN (data.nominal_type) > align)
>             align = TYPE_ALIGN (data.passed_type);
> data.passed_type has already been used in FUNCTION_BOUNDARY computation, so it
> really surprises me it doesn't use nominal_type's TYPE_ALIGN instead.

You may have an unaligned parameter. If it is spilled onto stack,
stack should be properly aligned. It isn't a problem for DImode.
But it may be a problem for other types. There may be some testcases
aleady to test it. If not, I can add a few.

What happened is we find DImode and try to align stack. At the
last minute, we find it isn't spilled and we skip the stack
alignment. What we need it is MINIMUM_TYPE_ALIGN, which is
the minimum alignment for a type. MINIMUM_TYPE_ALIGN should
be the same as TYPE_ALIGN. But on IA32, MINIMUM_TYPE_ALIGN (DImode)
== 4 and TYPE_ALIGN (DImode) == 8. We can use MINIMUM_TYPE_ALIGN
for stack alignment.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40667