https://llvm.org/bugs/show_bug.cgi?id=23744
Bug ID: 23744
Summary: Less efficient encoding of and using direct object
emission
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: MC
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
"and" has a less efficient encoding when using direct object emission, compared
to outputting assembly (-O1/2/3).
Found with running check_cfc.py dash_s_no_change on the llvm-test-suite
(r238815).
Reduced from function_try_block.cpp
$ cat test.cpp
static int a;
void fn1() {
if (a)
a = 0;
a = 1;
}
$ clang++ -O1 -c test.cpp && objdump -d test.o
test.o: file format elf64-x86-64
...
0000000000000000 <_Z3fn1v>:
0: 0f b6 05 00 00 00 00 movzbl 0x0(%rip),%eax # 7 <_Z3fn1v+0x7>
7: 25 01 00 00 00 and $0x1,%eax
...
$ clang++ -O1 -c test.cpp -via-file-asm && objdump -d test.o
test.o: file format elf64-x86-64
...
0000000000000000 <_Z3fn1v>:
0: 0f b6 05 00 00 00 00 movzbl 0x0(%rip),%eax # 7 <_Z3fn1v+0x7>
7: 83 e0 01 and $0x1,%eax
...
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