[tree-ssa]: Easy way to get default def of a variable?

[Daniel Berlin]

On Wednesday, June 4, 2003, at 06:22  PM, Andrew MacLeod wrote:

> On Wed, 2003-06-04 at 16:48, Daniel Berlin wrote:
>> Sometimes, when doing injury insertions, we need to know the default
>> definition of a variable.
>
> Whats an injury insertion?

Injury repairs for strength reduction injuries.

Given:

a = b + 6;
b = b + 9;
a = b + 6;

Normally, the definition of b would *kill* the expression "b + 6", so 
that we couldn't remove the second one.
With strength reduction extensions to PRE, the update to b only 
*injures* the definition of b, and we repair it later.
IE we transform it into
pretmp = b + 6
a = pretmp
pretmp = pretmp + 9
a = pretmp.

I didn't actually mean injury insertion, i meant code insertion, i was 
just working on the strength reduction code at the time, so it slipped 
in there.
>
>> IE the first version of the variable.
>>
>
> The first version of all variables, or just the the versions which are 
> a
> use of a variable which doesn't have a definition?

So far, the second.
No telling i won't run into the first case, however.

> Meaning that it is
> live on entry to the function?
>
In this case i'm looking at, it's actually one of the function 
parameters, so yes.

If we renamed them in the FUNCTION_DECL's DECL_ARGUMENS temporarily, 
and dropped the SSA name tree on out-of-ssa, i could just look there.

> Andrew
>