https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63475
Uroš Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
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CC| |law at gcc dot gnu.org
--- Comment #1 from Uroš Bizjak <ubizjak at gmail dot com> ---
Whoa.
VALUE RTXes are leaking into various RTX aliasing related functions like crazy!
As an example, please consider following patch for base_alias_check:
--cut here--
Index: alias.c
===================================================================
--- alias.c (revision 216025)
+++ alias.c (working copy)
@@ -1824,6 +1824,13 @@ base_alias_check (rtx x, rtx x_base, rtx y, rtx y_
if (rtx_equal_p (x_base, y_base))
return 1;
+ if (GET_CODE (x) == VALUE || GET_CODE (y) == VALUE)
+ {
+ debug_rtx (x);
+ debug_rtx (y);
+ gcc_unreachable ();
+ }
+
/* The base addresses are different expressions. If they are not accessed
via AND, there is no conflict. We can bring knowledge of object
alignment into play here. For example, on alpha, "char a, b;" can
--cut here--
The compiler dies immediately on the provided testcase.
One of the checks that trigger this condition in base_alias_check is:
(and:DI (lo_sum:DI (reg/f:DI 13 $13 [72])
(symbol_ref:DI ("aaa") [flags 0x6] <var_decl 0x2b66ff7cb000 aaa>))
(const_int -8 [0xfffffffffffffff8]))
with
(value:DI 7:3304360 @0x1b619ee0/0x1b614cb0)
and this is the reason why aliasing of aaa and bbb is not detected. The (VALUE)
RTX corresponds to:
cselib value 7:3304360 0x8a84cb0 (and:DI (lo_sum:DI (reg/f:DI 11 $11 [78])
(symbol_ref:DI ("bbb") [flags 0x6] <var_decl 0x2b2ff8af6090 bbb>))
(const_int -8 [0xfffffffffffffff8]))
so, there is no way for current code to detect aliasing between these two
RTXes.
This is IMO important RTL infrastructure problem.
