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Re: Ada subtypes and base types
- From: Sebastian Pop <sebastian dot pop at cri dot ensmp dot fr>
- To: Richard Kenner <kenner at vlsi1 dot ultra dot nyu dot edu>
- Cc: law at redhat dot com, gcc at gcc dot gnu dot org
- Date: Fri, 24 Feb 2006 18:42:11 +0100
- Subject: Re: Ada subtypes and base types
- References: <10602241616.AA08086@vlsi1.ultra.nyu.edu>
Richard Kenner wrote:
> Just to make sure I've dotted the i's and crossed the t's, this is not
> what's happening when we hang in VRP when compiling a-textio.
> We convert the incoming object from natural___XDLU_0___2147483647
> into its base type, perform the addition in the base type, then
> convert back to XDLU_0_2147483647.
> The above is exactly what I thought everybody agrees is and should be
> happening, so I'm confused by your "this is not what's happening"
> comment above.
So if I understand correctly, if we can prove that the operation does
not overflow in natural___XDLU_0___2147483647, then there is no need
of a cast to the base type and back.
chrec_convert is checking for non overflowing sequences before
removing a cast, and that is missing from the aggressive convert.
Aggressive convert has been intentionally implemented this way because
the conservative chrec_convert has caused performance regressions (see
sixtrack slowdowns from last August).
A patch like the following would solve the problem too, but will
introduce performance regressions... so I'm not sure that it is a good
--- tree-chrec.c (revision 111416)
+++ tree-chrec.c (working copy)
@@ -1202,6 +1202,8 @@ chrec_convert_aggressive (tree type, tre
tree inner_type, left, right, lc, rc;
+ return chrec_convert (type, chrec, NULL_TREE);
if (automatically_generated_chrec_p (chrec)
|| TREE_CODE (chrec) != POLYNOMIAL_CHREC)