https://bugs.llvm.org/show_bug.cgi?id=43252
Bug ID: 43252
Summary: Unnecessary mov instruction
Product: clang
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: -New Bugs
Assignee: unassignedclangb...@nondot.org
Reporter: tspit...@ieee.org
CC: htmldevelo...@gmail.com, llvm-bugs@lists.llvm.org,
neeil...@live.com, richard-l...@metafoo.co.uk
For the following code
void foo(int i);
void bar(int i) {
if (i != 0)
foo(i);
bar(i);
}
clang -O3 -S produces this (cleaned up)
bar:
pushq %rbx
movl %edi, %ebx
testl %edi, %edi
je .LBB0_2
movl %ebx, %edi
callq foo
.LBB0_2:
movl %ebx, %edi
popq %rbx
jmp foo
The marked mov instruction is not necessary, as edi is already equal to ebx.
Also, the LBB0_2 label can move down one line to just before the popq
instrucion, as if the branch is taken then edi is still equal to ebx.
This is for clang 8.0 on Fedora 30. clang --version produces
clang version 8.0.0 (Fedora 8.0.0-1.fc30)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
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