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From: "law at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/60131] [4.9 Regression] RTL check fail in rhs_regno
Date: Mon, 10 Feb 2014 19:03:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60131

--- Comment #4 from Jeffrey A. Law <law at redhat dot com> ---
The problem here is we first have the following candidate and defining insn:

gdb) p debug_rtx (cand->insn)
(insn 24 23 25 6 (set (reg:DI 0 ax [orig:100 D.2269 ] [100])
        (zero_extend:DI (reg/v:SI 0 ax [orig:91 v ] [91]))) j.c:22 133
{*zero_extendsidi2}
     (nil))
$13 = void
(gdb) p debug_rtx (curr_insn)
(insn 33 32 35 7 (set (reg/v:SI 0 ax [orig:91 v ] [91])
        (sign_extend:SI (reg:HI 0 ax [orig:88 D.2271 ] [88]))) j.c:19 146
{extendhisi2}
     (nil))

We eliminate insn 24 by changing insn 33 into:

(insn 33 32 35 7 (set (reg:DI 0 ax)
        (zero_extend:DI (sign_extend:SI (reg:HI 0 ax [orig:88 D.2271 ] [88]))))
j.c:19 -1
     (nil))


Later we call combine_reaching_defs to see if we can eliminate insn 33.  It now
has an unexpected form and we trigger the checking fault.