https://bugs.llvm.org/show_bug.cgi?id=40646
Bug ID: 40646
Summary: cmov regression
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: antonin.k...@gmail.com
CC: llvm-bugs@lists.llvm.org
Created attachment 21443
--> https://bugs.llvm.org/attachment.cgi?id=21443&action=edit
simple source file
clang has stopped using cmov instruction in the following
case(https://godbolt.org/z/CvPhJo)
clang-trunk:
offset(ctx&, unsigned long):
mov rax, qword ptr [rdi + 8]
mov rcx, qword ptr [rdi + 16]
sub rax, rcx
cmp rax, rsi
setae al
jae .LBB0_1
mov rcx, qword ptr [rdi]
mov qword ptr [rdi], rcx
ret
.LBB0_1:
add rcx, rsi
mov qword ptr [rdi], rcx
ret
clang-5:
offset(ctx&, unsigned long):
mov rax, qword ptr [rdi + 8]
mov rcx, qword ptr [rdi + 16]
sub rax, rcx
add rcx, rsi
cmp rax, rsi
setae al
cmovb rcx, qword ptr [rdi]
mov qword ptr [rdi], rcx
ret
gcc-trunk:
offset(ctx&, unsigned long):
mov rdx, QWORD PTR [rdi+16]
mov rcx, QWORD PTR [rdi+8]
sub rcx, rdx
cmp rsi, rcx
setbe al
add rdx, rsi
cmp rsi, rcx
cmova rdx, QWORD PTR [rdi]
mov QWORD PTR [rdi], rdx
ret
Maybe there is a good reason why clang is not using cmov but according to this
measurement https://github.com/xiadz/cmov, cmov seems to be the better choice.
--
You are receiving this mail because:
You are on the CC list for the bug._______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
