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

Kenneth Zadeck <> writes:
> 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.

Right.  is_sign_extended is only useful if it's a compile-time value.
Making it a run-time value would negate the benefit.

I think in practice STORE_FLAG_VALUE is a compile-time constant too,
so we could set is_sign_extended to STORE_FLAG_VALUE == -1.  But AFAICT
that would only help SPU and m68k.

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

You mean the one in the assert?  Yeah, OK.  How about this version?


Index: gcc/rtl.h
--- gcc/rtl.h	2013-11-02 11:06:12.738517644 +0000
+++ gcc/rtl.h	2013-11-02 14:22:05.636007860 +0000
@@ -1408,7 +1408,9 @@ typedef std::pair <rtx, enum machine_mod
     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 &);
@@ -1432,7 +1434,8 @@ wi::int_traits <rtx_mode_t>::decompose (
     case CONST_INT:
       if (precision < HOST_BITS_PER_WIDE_INT)
 	gcc_checking_assert (INTVAL (x.first)
-			     == sext_hwi (INTVAL (x.first), precision));
+			     == sext_hwi (INTVAL (x.first), precision)
+			     || (precision == 1 && INTVAL (x.first) == 1));
       return wi::storage_ref (&INTVAL (x.first), 1, precision);

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