ubsan PATCH to fix compile-time hog with operator overloading (PR sanitizer/78208)

[Jakub Jelinek]

On Fri, Nov 04, 2016 at 05:05:51PM +0100, Marek Polacek wrote:
> This is a similar case to PR sanitizer/70342.  Here, we were generating expression
> in a quadratic fashion because of the initializer--we create SAVE_EXPR <>, then 
> UBSAN_NULL <SAVE_EXPR <>>, and then COMPOUND_EXPR of these two and so on.
> 
> On this testcase we were instrumention CALL_EXPR that is in fact operator<<.  I
> think those always return a reference, so it cannot be NULL, so there's no
> point in instrumenting those?

How do you know what is the return type of a user defined overloaded
operator?
Even when it returns a reference, I thought the point of -fsanitize=null was
for all references to verify their addresses are non-null.

I must say I don't understand the issue, if it is the same SAVE_EXPR in both
lhs of COMPOUND_EXPR and UBSAN_NULL argument, shouldn't cp_genericize_r use
of hash table to avoid walking the same tree multiple times avoid the
exponential compile time/memory?

> Bootstrapped/regtested on x86_64-linux, ok for trunk?
> 
> 2016-11-04  Marek Polacek  <polacek@redhat.com>
> 
> 	PR sanitizer/78208
> 	* cp-gimplify.c (cp_genericize_r): Don't instrument
> 	CALL_EXPR_OPERATOR_SYNTAX.
> 
> 	* g++.dg/ubsan/null-8.C: New.
> 
> diff --git gcc/cp/cp-gimplify.c gcc/cp/cp-gimplify.c
> index 9b9b511..f39e9d5 100644
> --- gcc/cp/cp-gimplify.c
> +++ gcc/cp/cp-gimplify.c
> @@ -1495,7 +1495,8 @@ cp_genericize_r (tree *stmt_p, int *walk_subtrees, void *data)
>  		= TREE_CODE (fn) == ADDR_EXPR
>  		  && TREE_CODE (TREE_OPERAND (fn, 0)) == FUNCTION_DECL
>  		  && DECL_CONSTRUCTOR_P (TREE_OPERAND (fn, 0));
> -	      if (flag_sanitize & (SANITIZE_NULL | SANITIZE_ALIGNMENT))
> +	      if (flag_sanitize & (SANITIZE_NULL | SANITIZE_ALIGNMENT)
> +		  && !CALL_EXPR_OPERATOR_SYNTAX (stmt))
>  		ubsan_maybe_instrument_member_call (stmt, is_ctor);
>  	      if ((flag_sanitize & SANITIZE_VPTR) && !is_ctor)
>  		cp_ubsan_maybe_instrument_member_call (stmt);

	Jakub