[Mesa-dev] [PATCH 0/6] glsl: Add support for switch statements

[Dan McCabe]

Comments at the end (where they are supposed to be :).

On 06/17/2011 05:54 PM, Dan McCabe wrote:
> There are three changes from the patch set I published on 6/15:
> 1) Removed IR pointers from AST classes and moved them to 
> glsl_parser_state,
> 2) Manage the new IR in a stack-like manner to properly handle 
> nesting, and
> 3) Squash 6/7 and 7/7 together, since both deal with IR generation
>
> #1 was in response to the concerns Kenneth expressed from his code 
> review on 6/15 about embedding IR data into AST structures.
>
> #2 was need as a consequence of #1 to support nested switch statements 
> correctly.
>
> #3 is a minor cosmetic change that merges the final implicit break IR 
> insertion into the larger collection of IR changes.
>
> cheers, danm
>
> On 06/17/2011 05:43 PM, Dan McCabe wrote:
>> This patch set adds support for switch statements to the GLSL 
>> compiler. We
>> modify the grammar for the compiler with productions for switch 
>> statements
>> and case labels, while adding supporting supporting productions not 
>> already
>> present. New AST classes are defined to support those productions. 
>> However,
>> with our apporach no new IR is needed, allowing us to leverage all 
>> existing
>> optimizations and code generation.
>

A foolish inconsistency is the hobgoblin of small minds.

Anyway, I just sent out pass 3 of this patch set. It now consists of 5 
(not 6) pieces. Parts 4/6 and 5/6 got mashed together into 4/5, but 
that's not a big deal since the former part 5/6 was simply fleshing out 
print support for the AST.

This change set has mostly minor, cosmetic changes. UNTIL part 5/5. The 
major issue that idr identified concerning nested loops should now be 
resolved. Basically, the loop model for switch statements got tossed 
into the waste basket. The reason I used loops in the first place was to 
leverage code generation for break statements. Bad idea. I now generate 
different code for break statements that are under the influence of a 
switch statement.

Now, the switch statement is translated into straightforward 
if/then/else IR.

In addition to maintaining internal state for the cached test value and 
the fall through state, I now additionally maintain a break state, which 
is initialized to false and set to true whenever a break stmt is 
executed. Prior to executing any case statements (the statements 
following a case label), the fallthru state is reset if the break state 
is enabled, inhibiting entry of the case statement block (which is 
guarded by the fallthru state).

A couple of other changes were replacing the if/then/elses used to 
maintain the fallthru and break states with conditional assignments. 
This actually simplified both the src code and the generated code.

As always, feedback is requested.

cheers, danm