<literal>import</literal> declaration
that does not explicitly list the entities brought into scope. For
example
+ </para>
<programlisting>
module M where
import X( f )
import Y
import qualified Z
p x = f x x
-<programlisting>
+</programlisting>
+ <para>
The <option>-fwarn-import-lists</option> flag will warn about the import
of <literal>Y</literal> but not <literal>X</literal>
If module <literal>Y</literal> is later changed to export (say) <literal>f</literal>,
ambiguous. No warning is produced for the import of <literal>Z</literal>
because extending <literal>Z</literal>'s exports would be unlikely to produce
ambiguity in <literal>M</literal>.
+ </para>
</listitem>
</varlistentry>
<para>We don't use a <option>-O*</option> flag for day-to-day
work. We use <option>-O</option> to get respectable speed;
e.g., when we want to measure something. When we want to go for
- broke, we tend to use <option>-O2 -fvia-C</option> (and we go for
+ broke, we tend to use <option>-O2</option> (and we go for
lots of coffee breaks).</para>
<para>The easiest way to see what <option>-O</option> (etc.)
</listitem>
</varlistentry>
- <varlistentry>
- <term><option>-monly-[32]-regs</option>:</term>
- <listitem>
- <para>(x86 only)<indexterm><primary>-monly-N-regs
- option (iX86 only)</primary></indexterm> GHC tries to
- “steal” four registers from GCC, for performance
- reasons; it almost always works. However, when GCC is
- compiling some modules with four stolen registers, it will
- crash, probably saying:
-
-<screen>
-Foo.hc:533: fixed or forbidden register was spilled.
-This may be due to a compiler bug or to impossible asm
-statements or clauses.
-</screen>
-
- Just give some registers back with
- <option>-monly-N-regs</option>. Try `3' first, then `2'.
- If `2' doesn't work, please report the bug to us.</para>
- </listitem>
- </varlistentry>
</variablelist>
</sect1>