https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81110
Bug ID: 81110
Summary: tree-vrp optimize unsigned comparison to signed
Product: gcc
Version: 5.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: qian.liu at ingenic dot com
Target Milestone: ---
Target: mips-linux-gnu mipsel-linux-gnu
Created attachment 41567
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41567&action=edit
reduced testcase
The following testcase is miscompiled at -O2 on mips . An unsigned comparison
operation is optimized to a singed comparion instruciton. When d[0] and d[1]
large enough, will get error result.
unsigned short d[2];
int DiffInt ()
{
if ((unsigned long)(65536*d[1]+d[0]) < (1<<28)){
return -1;
}
}
Currently assembly:
li $3,268435456 # 0x10000000
slt $2,$2,$3 # error
beq $2,$0,$L4
But expected：
li $3,268435456 # 0x10000000
sltu $2,$2,$3 # unsigned
beq $2,$0,$L4
In tree-vrp dump file test.c.081t.vrp1, unsigned _8 is simplifed to singned _7.
But this is incorrect.
int _7;
long unsigned int _8;
.....
_8 = (long unsigned int) _7;
- if (_8 <= 268435455)
+ if (_7 <= 268435455)
