https://llvm.org/bugs/show_bug.cgi?id=23673
Bug ID: 23673
Summary: more optimize oppotunity
Product: clang
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: -New Bugs
Assignee: unassignedclangbugs at nondot.org
Reporter: ishiura-compiler at ml.kwansei.ac.jp
CC: llvmbugs at cs.uiuc.edu
Classification: Unclassified
We compiled a program (A.c) by LLVM/Clang-3.7.0 and GCC-6.0.0 with -O3 option.
GCC performed better optimization on this code, where the code for the
expression for t (which always evaluates to 1) is eliminated.
(A.c)
int x = -1;
int main (void)
{
int t = ((((0!=(1*(x+1)))<<0U)/-2344)|1);
if (t == 1) ;
else __builtin_abort();
return 0;
}
+------------------------------------------------------------+--------------------------------------------------------+
| gcc.s (gcc A.c -O3 -S) |
clang.s (clang A.c -O3 -S) |
+------------------------------------------------------------+--------------------------------------------------------+
|main: |
*
|.LFB11: |main:
# @main *
| .cfi_startproc |
.cfi_startproc |
| |# BB#0:
# %entry *
| | pushq
%rax *
| |.Ltmp0:
*
| |
.cfi_def_cfa_offset 16 *
| | cmpl
$-1, x247(%rip) *
| | setne
%al *
| | movzbl
%al, %eax *
| | negl
%eax *
| | movl
%eax, %ecx *
| | shrl
$31, %ecx *
| | sarl
$11, %eax *
| | addl
%ecx, %eax *
| | orl
$1, %eax *
| | cmpl
$1, %eax *
| | jne
.LBB0_2 *
| |# BB#1:
# %if.end *
| xorl %eax, %eax | xorl
%eax, %eax |
| ret | popq
%rdx *
| | retq
*
| |.LBB0_2:
# %if.else *
| | callq
abort *
| |.Ltmp1:
*
| | .size
main, .Ltmp1-main *
| .cfi_endproc |
.cfi_endproc |
|.LFE11: |
*
| .size main, .-main | .type
x247, at object # @x247 *
| .section .text.unlikely |
|
|.LCOLDE0: |
|
| .section .text.startup |
|
|.LHOTE0: |
|
| .globl x247 |
|
| .data | .data
|
| .align 4 | .globl
x247 *
| .type x247, @object | .align 4
*
| .size x247, 4 |
|
|x247: |x247:
|
| .long -1 | .long
4294967295 # 0xffffffff *
| | .size
x247, 4 *
+------------------------------------------------------------+--------------------------------------------------------+
clang version 3.7.0 (trunk 237801)
Target: x86_64-unknown-linux-gnu
Thread model: posix
gcc (GCC) 6.0.0 20150416 (experimental)
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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