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A comment on Stop Memsetting Structures. Parent comment

Re:Stop Memsetting Structures by jcr1488 on Wednesday May 01, 2019 @08:38AM (#19796494)
> That step is 90% of the work

I spent several years working on a production grade compiler and I can assure you it's not. But keep just making things up off the top of your head if it makes you feel smart.

[ Parent | on HN ]
Re:Stop Memsetting Structures by Dylan16807 on Wednesday May 01, 2019 @06:02PM (#19802114)
Would you care to explain why?

Let's look at a basic common case, as a checklist.

1. All fields are definitely assigned.

2. No functions are called except intrisics.

3. Nothing reads from the object on any control path.

4. Memset happens between creation and first assignment.

We agreed that step 1 is a solved problem, right? Are any of 2-4 difficult? Did I miss any prerequisites for the optimization?

Once you can prove 1-4, isn't the optimization pass as simple as looking for memsets applied to structs, checking 1-4, then deleting the call?

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