Re: Useless code generated by gcc 2.95.2????

["Martin v. Loewis" <martin at mira dot isdn dot cs dot tu-berlin dot de>]

> 	We are looking to upgrade from egcs 1.0.2 to gcc 2.95.2, and
> we noticed that object file sizes have gone up significantly (~50%)
> between the two releases (On Sparc).  So, I thought I would take a
> look at some of the generated asm. I noticed what looked to be dead
> code that was generated. Based on my observations I have generated a
> small test case:


Thanks for your bug report. My (shallow) analysis agrees with yours;
it indeed appears that this is dead code. Notice how the code
following LL5 is similar to the one following LL3.

I have not tried to understand in detail why this code is emitted. It
could be either a duplication of exception handlers, or it could be
cover some case that does not appear in your example.

Please understand that I'm not terribly worried about this code. I
compiled your code with optimization (-O2); the assembler code
generated for that is attached. Long and obfuscated machine code in
non-optimizing mode is not strictly a bug - incorrect code would be a
bug. Also, dead code in optimizing mode could be a bug.

If you want to understand in detail why this code is generated, you
may try using the "-da" option. This dumps a number of internal
structures (RTL) into files. Those structures are later used to
generate assembler output.

Hope this helps,
Martin

reset__Fv:
.LLFB1:
	!#PROLOGUE# 0
	save	%sp, -112, %sp
.LLCFI0:
	!#PROLOGUE# 1
	mov	1, %o0
	call	__builtin_new, 0
	sethi	%hi(fu8), %l0
	st	%o0, [%l0+%lo(fu8)]
	ret
	restore
.LLFE1:
.LLfe1:
	.size	 reset__Fv,.LLfe1-reset__Fv