https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103046
Bug ID: 103046
Summary: Incorrect debug info for uint128 bit shift in gcc 11.2
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: liyd2021 at gmail dot com
Target Milestone: ---
Affected versions: gcc 11.2.0 with gdb (Ubuntu 20.04.2)
gcc11.2 generates wrong debug when left shift uint128 value for more than 64
bits.
The debug info shows variable `a` has a const value `0xff00...` while the
actual value of `a` is `0x0100...`
This bug cannot be reproduced in gcc 10 or 9.
(terminal) $ cat a.c && gcc -g -Og a.c
typedef unsigned __int128 U;
__attribute__((noipa)) void foo(U x) {}
int main() {
U a = (U) 1 << 120;
foo(a);
}
--------------------
(terminal) $ cat run.gdb
b 7
b foo
r
p/x a
c
p/x x
--------------------
(terminal) $ gdb -x run.gdb a.out
Breakpoint 1 at 0x40116e: file a.c, line 7.
Breakpoint 2 at 0x401169: file a.c, line 3.
Breakpoint 1, main () at a.c:7
7 foo(a);
$1 = 0xff000000000000000000000000000000 <- **BUG**: wrong value
Breakpoint 2, foo (x=1329227995784915872903807060280344576) at a.c:3
3 __attribute__((noipa)) void foo(U x) {}
$2 = 0x1000000000000000000000000000000 <- correct value
--------------------
debug info and assembly:
<2><61>: Abbrev Number: 5 (DW_TAG_variable)
<62> DW_AT_name : a
<64> DW_AT_decl_file : 1
<65> DW_AT_decl_line : 6
<66> DW_AT_decl_column : 7
<67> DW_AT_type : <0x2e>
<6b> DW_AT_const_value : 0xff000000000000000000000000000000
