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Re: [PATCH] Fix overzealous folding
> Eric, would you please look into this
Already done, please re-read the thread.
> and work out what we really ought to be doing here?
Already done as well: properly disable the folding or rewrite VRP to avoid
taking advantage of TYPE_MIN/MAX_VALUE.
> And, would you please add a comment to the code that you changed that
> indicates that the exclusion of ENUMERAL_TYPEs is a work-around, with a
> link to the PR so that we know why?
Here's what I've installed on the mainline. The exclusion of BOOLEAN_TYPE has
been there from day #1 apparently.
Index: fold-const.c
===================================================================
--- fold-const.c (revision 136136)
+++ fold-const.c (working copy)
@@ -7866,7 +7866,10 @@ fold_unary (enum tree_code code, tree ty
/* Convert (T)(x & c) into (T)x & (T)c, if c is an integer
constants (if x has signed type, the sign bit cannot be set
- in c). This folds extension into the BIT_AND_EXPR. */
+ in c). This folds extension into the BIT_AND_EXPR.
+ ??? We don't do it for BOOLEAN_TYPE or ENUMERAL_TYPE because they
+ very likely don't have maximal range for their precision and this
+ transformation effectively doesn't preserve non-maximal ranges. */
if (TREE_CODE (type) == INTEGER_TYPE
&& TREE_CODE (op0) == BIT_AND_EXPR
&& TREE_CODE (TREE_OPERAND (op0, 1)) == INTEGER_CST)
--
Eric Botcazou