Bug#472867: gcc-4.3: gcc regression in optimization (4.2 -> 4.3)

[Cyprien LAPLACE <cyprien+debianbug@cypou.net>]

Package: gcc-4.3
Version: 4.3.0-2
Severity: grave
Justification: renders package unusable


gcc-4.3 forgets some checks in -O2 and -O3, tested on x86_64 and arm
(cross-compiler) targets.

the following is an exemple code with disassembled generated code by
gcc for 4.2 and 4.3 versions:


/* a.c */

int main()
{
  register char (*foo)[32] = (void*)0xffff8000;
  do {
    asm volatile("mov %0, %0"::"r"(foo));
  } while(++foo);
  return (long)**foo;
}

/******* gcc 4.2 ********

 * gcc-4.2 -c a.c -O2
 * objdump -d a.o

a.o:     file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <main>:
   0:   b8 00 80 ff ff          mov    $0xffff8000,%eax
   5:   48 89 c0                mov    %rax,%rax
   8:   48 83 c0 20             add    $0x20,%rax
   c:   75 f7                   jne    5 <main+0x5>
   e:   0f be 04 25 00 00 00    movsbl 0x0,%eax
  15:   00 
  16:   c3                      retq   


 * arm-linux-gnueabi-gcc-4.2 -c a.c -O3
 * arm-linux-gnueabi-objdump -d a.o

a.o:     file format elf32-littlearm

Disassembly of section .text:

00000000 <main>:
   0:	e59f3010 	ldr	r3, [pc, #16]	; 18 <main+0x18>
   4:	e1a03003 	mov	r3, r3
   8:	e2933020 	adds	r3, r3, #32	; 0x20
   c:	1afffffc 	bne	4 <main+0x4>
  10:	e5d30000 	ldrb	r0, [r3]
  14:	e12fff1e 	bx	lr
  18:	ffff8000 	.word	0xffff8000

 ******* gcc 4.3 ********

 * gcc-4.3 -c a.c -O2
 * objdump -d a.o

a.o:     file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <main>:
   0:   b8 00 80 ff ff          mov    $0xffff8000,%eax
   5:   0f 1f 00                nopl   (%rax)
   8:   48 89 c0                mov    %rax,%rax
   b:   48 83 c0 20             add    $0x20,%rax
   f:   eb f7                   jmp    8 <main+0x8>


 * arm-linux-gnueabi-gcc-4.3 -c a.c -O3
 * arm-linux-gnueabi-objdump -d a.o

a.o:     file format elf32-littlearm

Disassembly of section .text:

00000000 <main>:
   0:	e59f3008 	ldr	r3, [pc, #8]	; 10 <main+0x10>
   4:	e1a03003 	mov	r3, r3
   8:	e2833020 	add	r3, r3, #32	; 0x20
   c:	eafffffc 	b	4 <main+0x4>
  10:	ffff8000 	.word	0xffff8000

*/

-- System Information:
Debian Release: lenny/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)

Kernel: Linux 2.6.22-2-amd64 (SMP w/2 CPU cores)
Locale: LANG=fr_FR.UTF-8, LC_CTYPE=fr_FR.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages gcc-4.3 depends on:
ii  binutils            2.18.1~cvs20080103-1 The GNU assembler, linker and bina
ii  cpp-4.3             4.3.0-2              The GNU C preprocessor
ii  gcc-4.3-base        4.3.0-2              The GNU Compiler Collection (base 
ii  libc6               2.7-8                GNU C Library: Shared libraries
ii  libgcc1             1:4.3.0-2            GCC support library
ii  libgomp1            4.3.0-2              GCC OpenMP (GOMP) support library

Versions of packages gcc-4.3 recommends:
ii  libc6-dev                     2.7-8      GNU C Library: Development Librari

-- no debconf information