https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106609
Bug ID: 106609
Summary: [SH] miscompilation of loop involving noreturn call
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: sebastien.michell...@ens-lyon.fr
Target Milestone: ---
Created attachment 53452
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53452&action=edit
Minimal test case
GCC 12.1.0 generates incorrect code for loops that call into noreturn functions
starting at -O1. For example,
__attribute__((noreturn)) void g(void);
void f(int *values)
{
for(int i = 0; i < 8; i++)
if(values[i] != 0) g();
}
gets compiled into
sts.l pr,@-r15
mov #8,r1
.L3: bt.s .L2
dt r1
mov.l .L5,r1 # _g
jsr @r1
nop
.L2: bf .L3
lds.l @r15+,pr
rts
nop
which has the obvious issue of not reading its input, and also using the T bit
through bt.s before doing any test.
I suppose this is an overly aggressive loop/CFG optimization, but I was not
able to trim it down as unfolding -O1 into the list of optimizations provided
by -Q --help=optimizers produced a completely different program. The bug still
occurs with -fno-aggressive-loop-optimizations at least.
With -funroll-all-loops, instead of 8 mov.l/tst/bf I just get 8 bf which
suggests that the test is wrongly eliminated causing the load to become dead.
Found in:
GCC 12.1.0
Commit 4991e2092 of today's master
Not found in:
GCC 11.1.0
Configured with:
../gcc-12.1.0/configure --prefix=$PREFIX --target=sh3eb-elf
--enable-languages=c --without-headers
Reproduction instructions:
$PREFIX/bin/sh3eb-elf-gcc -S noreturn-loop-bug.c -o - -O1
