r199302 - CodeGen: Simplify CodeGenFunction::EmitCaseStmt

[Justin Bogner]

Chris Lattner <clattner at apple.com> writes:
> On Jan 15, 2014, at 12:21 AM, Justin Bogner <mail at justinbogner.com> wrote:
>>> Hold on, I don't think that's the right way to interpret this.
>>> 
>>> Allocating, wiring up, optimizing and deleting the block all have very
>>> non-trivial compile-time cost. They introduce guaranteed malloc traffic.
>>> Worse, linear amounts of malloc traffic.
>
> Yes, what Chandler said.  My understanding is that you were going to
> change it to emit the “dead” blocks for the specific purpose of
> putting a counter in them (which is how it already was).
>
>> I hadn't thought about this point, but as far as "how this came to be" I
>> don't think that there's any other way to interpret it. r129652
>> specifically calls this "a -O0 code quality issue" in its commit
>> message.
>> 
>> From a programmer's perspective, letting the backend clean up these
>> blocks means less duplicated logic, and in my experience that means
>> fewer bugs. That said, I don't have a deep understanding of the cost for
>> the backend to remove empty blocks.
>
> You’re optimizing for the wrong thing.  Yes, it is good to avoid
> duplicated code in the compiler when all things are equal, but here
> all things are not equal: you’re making the compiler slower for
> *users* of the compiler.

Sorry, I guess I misunderstood. I've reverted this change in r199700.