Re: c++ 2.97, warning: ICE: would have deleted prologue/epilogue insn

[Ralf Baechle <ralf at oss dot sgi dot com>]

Here is a smaller test case in plane C without includes that results in the
same error message.  Note that the size of the array stack[] seems to be
a magic factor.  The ICE only happens if it's larger than 8188 elements
that is the resulting total stack frame is larger than 32kb.

As I interpret this case;

 - The instruction represented by the patern isn't actually part of the
   epilogue but of the function body.
 - The instruction is really dead code and should be removed.
 - The warning is bogus.

[root@babe redhat]# cat sit.c
void sit_mw_out(void)
{
	int stack_ptr;
	int stack[16384];
	int ptr;

	ptr = stack[--stack_ptr];
}
[root@babe redhat]# gcc -O -S -dp sit.c
sit.c: In function `sit_mw_out':
sit.c:8: warning: ICE: would have deleted prologue/epilogue insn
(insn 42 40 43 (set (reg:SI 13 t5)
        (plus:SI (reg:SI 12 t4)
            (reg:SI 29 sp))) -1 (nil)
    (nil))
[root@babe redhat]# cat sit.s
	.file	1 "sit.c"
	.abicalls
	.version	"01.01"
gcc2_compiled.:
__gnu_compiled_c:
	.text
	.align	2
	.globl	sit_mw_out
	.ent	sit_mw_out
sit_mw_out:
	.frame	$sp,65552,$31		# vars= 65536, regs= 1/0, args= 0, extra= 8
	.mask	0x10000000,-8
	.fmask	0x00000000,0
	.set	noreorder
	.cpload	$25
	.set	reorder
	subu	$sp,$sp,65552
	.cprestore 0
	li	$13,65536			# 0x10000	 # 30	movsi_internal2/3	[length = 4]
	ori	$13,$13,0x8	 # 32	anddi3_internal1+1/2	[length = 4]
	addu	$13,$13,$sp	 # 34	addsi3_internal	[length = 4]
	sw	$28,0($13)	 # 36	movsi_internal2/7	[length = 4]
	li	$12,65536			# 0x10000	 # 51	movsi_internal2/3	[length = 4]
	ori	$12,$12,0x10	 # 52	anddi3_internal1+1/2	[length = 4]
	addu	$13,$12,$sp	 # 42	addsi3_internal	[length = 4]
	.set	noreorder
	.set	nomacro
	j	$31	 # 46	return_internal	[length = 4]
	addu	$sp,$sp,$12	 # 45	addsi3_internal	[length = 4]
	.set	macro
	.set	reorder

	.end	sit_mw_out