[PATCH] Restore defensive check in tree_nop_conversion (also PR89779 "fix")

[Jason Merrill]

On 3/21/19 9:43 AM, Richard Biener wrote:
> On Thu, 21 Mar 2019, Richard Biener wrote:
> 
>>
>> This also avoids the ICE in PR89779 but IMHO is not a real fix.
>>
>> Still it restores a previously active check against released SSA names
>> which now have error_mark_node type rather than NULL.  The new way
>> opens up consolidation so I've adjusted tree_nop_conversion plus
>> operand_equal_p which got a defensive check at the same time
>> (and checks for error_mark_node right before that check).
>>
>> Bootstrap & regtest running on x86_64-unknown-linux-gnu.
>>
>> The testcase comes with the other patch (but still included below).
> 
> Ugh, looks like my defense installed for released SSA names is now
> relied upon by the C++ FE via
> 
> #2  0x0000000001864a96 in tree_strip_nop_conversions (
>      exp=<convert_expr 0x7ffff69bc920>)
>      at /space/rguenther/src/svn/trunk2/gcc/tree.c:12848
> #3  0x0000000000ab2d2f in iterative_hash_template_arg (
>      arg=<convert_expr 0x7ffff69bc920>, val=3363282904)
>      at /space/rguenther/src/svn/trunk2/gcc/cp/pt.c:1751
> 
> for
> 
>   <convert_expr 0x7ffff69bc920
>      type <integer_type 0x7ffff68985e8 int public type_6 SI
>          size <integer_cst 0x7ffff689c078 constant 32>
>          unit-size <integer_cst 0x7ffff689c090 constant 4>
>          align:32 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
> 0x7ffff68985e8 precision:32 min <integer_cst 0x7ffff689c030 -2147483648>
> max <integer_cst 0x7ffff689c048 2147483647>
>          pointer_to_this <pointer_type 0x7ffff68a19d8>>
>     
>      arg:0 <scope_ref 0x7ffff69d0b40 tree_0
>          arg:0 <template_type_parm 0x7ffff69d17e0 i tree_0 type_0 type_6
> VOID
>              align:8 warn_if_not_align:0 symtab:0 alias-set -1
> canonical-type 0x7ffff69d1150
>             index 0 level 1 orig_level 1
>              chain <type_decl 0x7ffff69d2098 i>>
>          arg:1 <identifier_node 0x7ffff69c39c0 c
>              normal local bindings <(nil)>>>>
> 
> where both the SCOPE_REF and TEMPLATE_TYPE_PARM have NULL
> TREE_TYPE.
> 
> So I'll restore the NULL check in tree_nop_conversion.
> 
> But since the C++ FE overloads almost every tree field possible
> I wonder whether that STRIP_NOPS in iterative_hash_template_arg
> is a good idea?

I think it still makes sense; TREE_TYPE of an expression is either a 
type, error_mark_node, or NULL_TREE (for type-dependent expressions in a 
template).

> Also I hope the FE doesn't call into operand_equal_p with such
> typed trees.

It shouldn't, we have cp_tree_equal to use instead.

Jason