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Re: [wide-int] Do not treat rtxes as sign-extended

On 11/02/2013 06:30 AM, Richard Sandiford wrote:
Bah.  After all that effort, it turns out that -- by design --
there is one special case where CONST_INTs are not sign-extended.
Nonzero/true BImode integers are stored as STORE_FLAG_VALUE,
which can be 1 rather than -1.  So (const_int 1) can be a valid
BImode integer -- and consequently (const_int -1) can be wrong --
even though BImode only has 1 bit.

It might be nice to change that, but for wide-int I think we should
just treat rtxes like trees for now.

Tested on powerpc64-linux-gnu and x86_64-linux-gnu.  It fixes some ICEs
seen on bfin-elf.  OK to install?
do we have to throw away the baby with the bath water here? I guess what you are saying is that it is worse to have is_sign_extended be a variable that is almost always true than to be a hard false.

also we could preserve the test and make it not apply to bimode.



Index: gcc/rtl.h
--- gcc/rtl.h	(revision 204311)
+++ gcc/rtl.h	(working copy)
@@ -1408,7 +1408,9 @@
      static const enum precision_type precision_type = VAR_PRECISION;
      static const bool host_dependent_precision = false;
-    static const bool is_sign_extended = true;
+    /* This ought to be true, except for the special case that BImode
+       is canonicalized to STORE_FLAG_VALUE, which might be 1.  */
+    static const bool is_sign_extended = false;
      static unsigned int get_precision (const rtx_mode_t &);
      static wi::storage_ref decompose (HOST_WIDE_INT *, unsigned int,
  				      const rtx_mode_t &);
@@ -1430,10 +1432,6 @@
    switch (GET_CODE (x.first))
      case CONST_INT:
-      if (precision < HOST_BITS_PER_WIDE_INT)
-	gcc_checking_assert (INTVAL (x.first)
-			     == sext_hwi (INTVAL (x.first), precision));
        return wi::storage_ref (&INTVAL (x.first), 1, precision);

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