optimizer bug in egcs-1.0.3a

[Bruno Haible <haible at ilog dot fr>]

Hi,

Here gcc simplifies two comparisons of the same term against adjacent
values into a single range check, but forgets that the range check is
to be done on a byte, not an int.

$ gcc -v
Reading specs from /usr/lib/gcc-lib/i486-pc-linux-gnulibc1/egcs-2.90.29/specs
gcc version egcs-2.90.29 980515 (egcs-1.0.3 release)
$ gcc foo32.c
$ ./a.out
$ gcc -O foo32.c
$ ./a.out
IOT trap/Abort (core dumped)

=============================== foo32.c ================================
void bar () {}
void baz () { abort(); }

void foo (unsigned int * p)
{
  if ((signed char)(*p & 0xFF) == 17 || (signed char)(*p & 0xFF) == 18)
    bar();
  else
    baz();
}

int main ()
{
  int i = 0x30011;
  foo(&i);
  return 0;
}
=========================== gcc -O -S foo32.c ==========================
	.file	"foo32.c"
	.version	"01.01"
/ GNU C version egcs-2.90.29 980515 (egcs-1.0.3 release) (i486-pc-linux-gnulibc1) compiled by GNU C version egcs-2.90.29 980515 (egcs-1.0.3 release).
/ options passed:  -O
/ options enabled:  -fdefer-pop -fthread-jumps -fpeephole -ffunction-cse
/ -finline -fkeep-static-consts -fpcc-struct-return -fcommon -fverbose-asm
/ -fgnu-linker -falias-check -fargument-alias -m80387 -mhard-float
/ -mno-soft-float -mieee-fp -mfp-ret-in-387 -mschedule-prologue -mcpu=i486
/ -march=pentium

gcc2_compiled.:
.text
	.align 16
.globl bar
	.type	 bar,@function
bar:
	pushl %ebp
	movl %esp,%ebp
	movl %ebp,%esp
	popl %ebp
	ret
.Lfe1:
	.size	 bar,.Lfe1-bar
	.align 16
.globl baz
	.type	 baz,@function
baz:
	pushl %ebp
	movl %esp,%ebp
	call abort
	.align 16
.Lfe2:
	.size	 baz,.Lfe2-baz
	.align 16
.globl foo
	.type	 foo,@function
foo:
	pushl %ebp
	movl %esp,%ebp
	movl 8(%ebp),%eax
	movl (%eax),%eax		; <=== These three instructions
	addl $-17,%eax			; <=== ignore the "& 0xFF"
	cmpl $1,%eax			; <=== present in the source
	ja .L4
	call bar
	jmp .L5
	.align 16
.L4:
	call baz
.L5:
	movl %ebp,%esp
	popl %ebp
	ret
.Lfe3:
	.size	 foo,.Lfe3-foo
	.align 16
.globl main
	.type	 main,@function
main:
	pushl %ebp
	movl %esp,%ebp
	subl $4,%esp
	movl $196625,-4(%ebp)
	leal -4(%ebp),%eax
	pushl %eax
	call foo
	xorl %eax,%eax
	movl %ebp,%esp
	popl %ebp
	ret
.Lfe4:
	.size	 main,.Lfe4-main
	.ident	"GCC: (GNU) egcs-2.90.29 980515 (egcs-1.0.3 release)"
========================================================================