[Bug other/93434] New: Miscompilation with -O3 starting from 8.1
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93434
Bug ID: 93434
Summary: Miscompilation with -O3 starting from 8.1
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: other
Assignee: unassigned at gcc dot gnu.org
Reporter: rlivings at mathworks dot com
Target Milestone: ---
We're working on upgrading our code base to GCC 8.3. In doing so one of our
tests started failing with a wrong answer. After narrowing down we see that the
code:
#include
typedef struct creal_T {
double re;
double im;
} creal_T;
#define N 16
int main() {
int k;
int i;
int j;
creal_T t2[N];
double inval;
inval = 1.0;
for (j = 0; j < N; ++j) {
t2[j].re = 0;
t2[j].im = 0;
}
for (j = 0; j < N/4; j++) {
i = j * 4;
t2[i].re = inval;
t2[i].im = inval;
/* Uncomment for correct behavior */
/* printf("t2[%d] = %g + %g*i\n", i, t2[i].re, t2[i].im); */
k = i + 3;
t2[k].re = inval;
t2[k].im = inval;
t2[i] = t2[k];
t2[k].re = inval;
}
printf("\n");
for (i = 0; i < 2; ++i) {
printf("t2[%2d] = %g + %g*i\n", i, t2[i].re, t2[i].im);
}
}
generates a binary that prints:
t2[ 0] = 0 + 1*i
t2[ 1] = 0 + 0*i
when compiled without warnings:
-O3 -Wall -Wextra -fno-strict-aliasing -fwrapv
in GCC 8.1 up through trunk. The -O2 and lower output is the correct answer:
t2[ 0] = 1 + 1*i
t2[ 1] = 0 + 0*i
Adding -fsanitize=undefined,address runs without error and returns the expected
answer.
Godbolt link for reference:
https://godbolt.org/z/uxVJ2K
gcc -v
Using built-in specs.
COLLECT_GCC=.../gcc-8.3.0/bin/gcc
COLLECT_LTO_WRAPPER=.../gcc-8.3.0/bin/../libexec/gcc/x86_64-pc-linux-gnu/8.3.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: .../gcc-8.3/configure --with-gmp=.../gcc-8.3/gmp-4.3
--with-mpfr=../gcc-8.3/mpfr --with-mpc=...gcc-8.3/mpc
--enable-languages=c,c++,fortran --enable-shared --enable-linker-build-id
--enable-plugin --enable-checking=release --enable-multiarch --enable-gold
--enable-ld=default --enable-libstdcxx-time=no --prefix=gcc-8.3.0
--with-pkgversion='MW GCC 8.3.0-gold' --with-tune=generic --with-system-zlib
--enable-multilib --with-multilib-list=m32,m64 --with-arch-directory=amd64
--with-arch-32=i586 --with-abi=m64
Thread model: posix
gcc version 8.3.0 (GCC 8.3.0-gold)
[Bug c/93435] New: Hang with -O2 on innocuous looking code with GCC 8.3
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93435
Bug ID: 93435
Summary: Hang with -O2 on innocuous looking code with GCC 8.3
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: rlivings at mathworks dot com
Target Milestone: ---
We're working on upgrading our code base to gcc 8.3 and hit a test which hung.
Upon further investigation the gcc invocation was hanging. A standalone repro
from that code is:
typedef signed char int8_T;
typedef int int32_T;
typedef struct {
int8_T a;
} struct0_T;
typedef struct {
struct0_T f10[4];
} struct_T;
typedef struct {
struct_T f9[4];
} b_struct_T;
typedef struct {
b_struct_T f8[4];
} c_struct_T;
typedef struct {
c_struct_T f7[4];
} d_struct_T;
typedef struct {
d_struct_T f6[4];
} e_struct_T;
typedef struct {
e_struct_T f5[4];
} f_struct_T;
typedef struct {
f_struct_T f4[4];
} g_struct_T;
typedef struct {
g_struct_T f3[4];
} h_struct_T;
typedef struct {
h_struct_T f2[4];
} i_struct_T;
typedef struct {
i_struct_T f1[4];
} j_struct_T;
typedef struct {
struct {
j_struct_T ds21[4];
i_struct_T ds20[4];
i_struct_T r9;
} f0;
} deep_struct_arraysStackData;
/* Function Definitions */
void deep_struct_arrays(deep_struct_arraysStackData *SD,
int8_T in1, int8_T inCount, int8_T *out1, int8_T *out2, struct0_T out3[4])
{
struct0_T r;
struct_T r1;
b_struct_T r2;
c_struct_T r3;
d_struct_T r4;
e_struct_T r5;
f_struct_T r6;
g_struct_T r7;
h_struct_T r8;
int32_T count;
int32_T i;
/* Check properties of input in1 */
/* Check properties of input inCount */
/* Copyright 2006 The MathWorks, Inc. */
r.a = in1;
r1.f10[0] = r;
r1.f10[1] = r;
r1.f10[2] = r;
r1.f10[3] = r;
r2.f9[0] = r1;
r2.f9[1] = r1;
r2.f9[2] = r1;
r2.f9[3] = r1;
r3.f8[0] = r2;
r3.f8[1] = r2;
r3.f8[2] = r2;
r3.f8[3] = r2;
r4.f7[0] = r3;
r4.f7[1] = r3;
r4.f7[2] = r3;
r4.f7[3] = r3;
r5.f6[0] = r4;
r5.f6[1] = r4;
r5.f6[2] = r4;
r5.f6[3] = r4;
r6.f5[0] = r5;
r6.f5[1] = r5;
r6.f5[2] = r5;
r6.f5[3] = r5;
r7.f4[0] = r6;
r7.f4[1] = r6;
r7.f4[2] = r6;
r7.f4[3] = r6;
r8.f3[0] = r7;
r8.f3[1] = r7;
r8.f3[2] = r7;
r8.f3[3] = r7;
SD->f0.r9.f2[0] = r8;
SD->f0.r9.f2[1] = r8;
SD->f0.r9.f2[2] = r8;
SD->f0.r9.f2[3] = r8;
SD->f0.ds20[0] = SD->f0.r9;
SD->f0.ds20[3] = SD->f0.r9;
count = 0;
while (count < inCount) {
i = in1 + SD->f0.ds20[0].f2[0].f3[0].f4[0].f5[0].f6[0].f7[0].f8[0].f9[0]
.f10[0].a;
if (i > 127) {
i = 127;
} else {
if (i < -128) {
i = -128;
}
}
SD->f0.ds20[0].f2[0].f3[0].f4[0].f5[0].f6[0].f7[0].f8[0].f9[0].f10[0].a =
(int8_T)i;
i = SD->f0.ds20[3].f2[3].f3[3].f4[3].f5[3].f6[3].f7[3].f8[3].f9[3].f10[3].a
+ 3;
if (i > 127) {
i = 127;
}
SD->f0.ds20[3].f2[3].f3[3].f4[3].f5[3].f6[3].f7[3].f8[3].f9[3].f10[3].a =
(int8_T)i;
count++;
}
if (inCount > 10) {
SD->f0.ds21[0].f1[1].f2[2].f3[3].f4[3].f5[3].f6[3].f7[3].f8[3].f9[3].f10[3].
a = 14;
} else {
SD->f0.ds21[0].f1[1].f2[2].f3[3].f4[3].f5[3].f6[3].f7[3].f8[3].f9[3].f10[3].
a = 16;
}
*out1 =
SD->f0.ds20[0].f2[0].f3[0].f4[0].f5[0].f6[0].f7[0].f8[0].f9[0].f10[0].
a;
*out2 =
SD->f0.ds20[3].f2[3].f3[3].f4[3].f5[3].f6[3].f7[3].f8[3].f9[3].f10[3].
a;
out3[0] = r;
out3[1] = r;
out3[2] = r;
out3[3] =
SD->f0.ds21[0].f1[1].f2[2].f3[3].f4[3].f5[3].f6[3].f7[3].f8[3].f9[3]
.f10[3];
}
That causes a hang when compiled with -O2. Adding in -Q gives:
gcc -O2 -Q -c foo.c
deep_struct_arrays
Analyzing compilation unit
Performing interprocedural optimizations
<*free_lang_data>
Assembling functions:
deep_struct_arrays {GC 401309k ->
221133k}
with no progress past that point. Adding in:
-Wall -Wextra -fno-strict-aliasing -fwrapv
shows no warnings and the same hang is observed.
gcc -v
Using built-in specs.
COLLECT_GCC=.../gcc-8.3.0/bin/gcc
COLLECT_LTO_WRAPPER=.../gcc-8.3.0/bin/../libexec/gcc/x86_64-pc-linux-gnu/8.3.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: .../gcc-8.3/configure --with-gmp=.../gcc-8.3/gmp-4.3
--with-mpfr=../gcc-8.3/mpfr --with-mpc=...gcc-8.3/mpc
--enable-languages=c,c++,fortran --enable-shared --enable-linker-build-id
--enable-plugin --enable-checking=release --enable-multiarch --enable-gold
--enable-ld=default --enable-libstdcxx-time=no --prefix=gcc-8.3.0
--with-pkgversion='MW GCC 8.3.0-gold' --with-tune=generic --with-system-zlib
--enable-multilib --with-multilib-list=m32,m64 --with-arch-directory=amd64
--with-arch-32=i586 --with-abi=m64
Thread model: posix
gcc version 8.3.0 (GCC 8.3.0-gold)
[Bug tree-optimization/93434] [8/9 Regression] Miscompilation with -O3 starting from 8.1
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93434 --- Comment #7 from Ryan Livingston --- Many thanks. The responsiveness here has been nothing short of impressive!
