[Fwd: BUG x86 define_expand "strlensi"]

[grahams <grahams at rcp dot co dot uk>]

Hi

I am resending this to the correct list.

grahams wrote:
> 
> All
> 
> I have been investigating problems with the define_expand "strlensi"
> pattern on the x86 and have come to the conclusion that it cannot
> use FAIL (i.e. it must expand or abort).
> 
> There are two reasons for coming to this conclusion
> 
> 1.) The expand_builtin_strlen () in builtins.c calls the MD
>     backend expander (i.e. gen_strlensi) using the following
> 
>         emit_insn (GEN_FCN (icode)(result, ...);
> 
>     If the MD gen_strlensi expander uses FAIL (can't expand) then
>     a NULL_RTX is returned and it make no sense to call emit_insn
>     with a NULL_RTX
> 
> 2.) Assuming the gen_strlensi () expander is correct in using
>     FAIL then the above code would need to be written
> 
>     expanded_rtx = GEN_FCN (icode)(result, ...);
>     if (!expanded_rtx)
>        return NULL_RTX;
>     emit_insn (expanded_rtx);
> 
>     But this in itself can causes aborts in expand_expr ()
>     if the rtl being expanded has a RTL_EXPR with a non-zero
>     RTL_EXPR_SEQUENCE ().
> 
>     The abort occurs because the when expand_expr processes a RTL_EXPR
>     with a non-zero RTL_EXPR_SEQUENCE() it finds it's value is const0_rtx.
> 
>     Note that when expand_expr processing a RTL_EXPR with a non zero
>     RTL_EXPR_SEQUENCE() has the side effect of setting the RTL_EXPR_SEQUENCE ()
>     to const0_rtx.
> 
>     I found that RTL_EXPR node was being expanded twice the 1st time via a
>     call to expand_expr() in expand_builtin_strlen() and subsequently if the
>     MD expander bailed out using FAIL a call to expand_expr() in expand_call().
> 
> This is an extract from i386.md file which shows its use of FAIL.
> 
> (define_expand "strlensi"  [(set (match_operand:SI 0 "register_operand" "")
>        (unspec:SI [(match_operand:BLK 1 "general_operand" "")
>                    (match_operand:QI 2 "immediate_operand" "")
>                    (match_operand:SI 3 "immediate_operand" "")] 0))]  ""
>  "
> {
> 
>   rtx out, addr, eoschar, align, scratch1, scratch2, scratch3;
> 
>   /* The generic case of strlen expander is long.  Avoid it's
>      expanding unless TARGET_INLINE_ALL_STRINGOPS.  */
> 
>   if (TARGET_UNROLL_STRLEN && eoschar == const0_rtx && optimize > 1
>       && !optimize_size
>       && (GET_CODE (align) != CONST_INT || INTVAL (align) < 4))
>     FAIL;
> 
> This code is using eoschar and align before they are initialized (
> reported this in a separate mailing to gcc-bugs a couple of days ago)
> 
> I don't understand how the comment matches the actual test performed?
> 
> I think this test should be deleted so that the expander always
> returns using DONE.
> 
> Comments anyone?
> 
> Graham