[Bug target/21715] New: code-generation regression

[markus at oberhumer dot com]

During recent performance testing I have identified a number of small code
fragments where gcc 4.x produces worse code than gcc 3.4.3. Some of these may be
target specific, and I plan to gradually enter such small performance
regressions into the bug database unless there is a better way to report these.


$ cat test.c
long foo(long v) { return v & -v; }

$ gcc-3.4.3 -O3 -c test.c && objdump -d test.o

test.o:     file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <foo>:
   0:   48 89 f8                mov    %rdi,%rax
   3:   48 f7 d8                neg    %rax
   6:   48 21 f8                and    %rdi,%rax
   9:   c3                      retq

$ gcc-4.1-20050516 -O3 -c test.c && objdump -d test.o

test.o:     file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <foo>:
   0:   48 89 f8                mov    %rdi,%rax
   3:   48 f7 d8                neg    %rax
   6:   48 21 c7                and    %rax,%rdi
   9:   48 89 f8                mov    %rdi,%rax
   c:   c3                      retq

-- 
           Summary: code-generation regression
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: markus at oberhumer dot com
                CC: gcc-bugs at gcc dot gnu dot org
  GCC host triplet: x86_64-pc-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21715