https://bugs.llvm.org/show_bug.cgi?id=39225
Bug ID: 39225
Summary: Failure to use condition to simplify branch
Product: new-bugs
Version: unspecified
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: llvm-...@redking.me.uk
CC: andrea.dibia...@gmail.com, fil...@gmail.com,
llvm-bugs@lists.llvm.org, llvm-bugzi...@jfbastien.com
https://godbolt.org/z/I7HTBx
void test(int &v, int i) {
if (v == i)
v = i;
}
clang -O3 -march=btver2
_Z4testRii: # @_Z4testRii
cmpl %esi, (%rdi)
jne .LBB0_2
movl %esi, (%rdi)
.LBB0_2:
retq
How come we couldn't remove this store and just return?
More complicated could also avoid some work:
void test1(int &v, int i, bool replace) {
if (replace || v == i)
v = i;
}
_Z5test1Riib: # @_Z5test1Riib
cmpl %esi, (%rdi)
je .LBB1_2
testb %dl, %dl
jne .LBB1_2
retq
.LBB1_2:
movl %esi, (%rdi)
retq
How come we couldn't just store based on the test?
int test3(int &v, int i, bool replace) {
if (replace || v == i) {
v = i;
return 1;
}
return 0;
}
_Z5test3Riib: # @_Z5test3Riib
cmpl %esi, (%rdi)
je .LBB2_2
xorl %eax, %eax
testb %dl, %dl
jne .LBB2_2
retq
.LBB2_2:
movl $1, %eax
movl %esi, (%rdi)
retq
Trickier, but we could avoid the store and just set the returncode:
_Z5test3Riib: # @_Z5test3Riib
cmpl %esi, (%rdi)
je .LBB2_3
xorl %eax, %eax
testb %dl, %dl
jne .LBB2_2
retq
.LBB2_2:
movl %esi, (%rdi)
.LBB2_3:
movl $1, %eax
retq
--
You are receiving this mail because:
You are on the CC list for the bug._______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
