https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103457
Bug ID: 103457
Summary: boolean operations on bit-fields are not merged
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: roland.illig at gmx dot de
Target Milestone: ---
~~~c
#include <stdbool.h>
typedef struct GNodeFlagsS {
bool remake:1;
bool childMade:1;
bool force:1;
bool doneWait:1;
bool doneOrder:1;
bool fromDepend:1;
bool doneAllsrc:1;
bool cycle:1;
bool doneCycle:1;
} GNodeFlags;
bool
GNodeFlags_IsNone(GNodeFlags flags)
{
return !flags.remake
&& !flags.childMade
&& !flags.force
&& !flags.doneWait
&& !flags.doneOrder
&& !flags.fromDepend
&& !flags.doneAllsrc
&& !flags.cycle
&& !flags.doneCycle;
}
~~~
On x86_64, GCC 11.2 generates:
~~~asm
GNodeFlags_IsNone(GNodeFlagsS):
mov eax, edi
and eax, 1
jne .L6
test dil, 2
jne .L1
mov eax, edi
shr ax, 2
and eax, 1
jne .L6
test dil, 8
jne .L1
mov eax, edi
shr ax, 4
and eax, 1
jne .L6
test dil, 32
jne .L1
mov eax, edi
shr ax, 6
and eax, 1
jne .L6
test dil, dil
js .L1
shr di, 8
mov eax, edi
and eax, 1
xor eax, 1
ret
.L6:
xor eax, eax
.L1:
ret
~~~
ICC 2021.3.0 generates shorter code:
~~~asm
test edi, 1 #18.10
jne ..B1.10 # Prob 50% #18.10
test edi, 2 #19.13
jne ..B1.10 # Prob 50% #19.13
test edi, 4 #20.13
jne ..B1.10 # Prob 50% #20.13
(and so on)
~~~
Many other compilers fail to see the potential for optimizing this code as
well.
Clang is better, it generates:
~~~asm
GNodeFlags_IsNone(GNodeFlagsS): # @GNodeFlags_IsNone(GNodeFlagsS)
test edi, 511
sete al
ret
~~~
