TREE_READONLY in lookup_tmp_var

[Richard Henderson]

On Fri, Aug 20, 2004 at 05:25:45PM -0400, Richard Kenner wrote:
>     They'll get the same variable when the expression is used with the
>     same inputs.  The inputs are not constrained such that they must
>     have the same values.  You'll notice that there is absolutely no
>     invalidation out of that hash table.
> 
>     It is a misunderstanding on your part what this is for -- the sole
>     purpose of this hash table is reducing the number of temporary
>     variables, not doing SSA or CSE.
> 
> No, you misunderstood me.

I understood you.  I then attempted to correct your misunderstanding.
Clearly it didn't work.

> If the hash table is giving, say, T.78 as the value of "X + Y" and T.78
> isn't really readonly (meaning it's modified), then another request
> for "X + Y" shouldn't give T.78 as that's no longer it's value.

We will return T.78 every single time you say "X + Y".  We then use the
value immediately and discard it.  These variables are not live across
sequence points.

I will repeat:

	... the sole
	purpose of this hash table is reducing the number of temporary
	variables, not doing SSA or CSE.


r~