Type-based alias analysis (-fstrict-aliasing) is only a small portion of the overall alias analysis. The basic baseline alias analysis and reasoning about memory even without AA is extremely important for basic optimizations / code movement, and there's no switch for disabling.
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You're saying that you want that all entirely disabled, with pointers treated as addresses. That's asking for a whole lot more than -fno-strict-aliasing and not marking pointer arithmetic inbounds (and the latter definitely has a huge impact on important loop optimizations, etc).
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I'm certainly not saying that it can't be done or that it isn't useful but that you're understating how much needs to be changed and the impact of it. Memory corruption also doesn't become predictable, just *less* impacted by optimization. It's still always going to be impacted.
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Here's something that's undefined: accessing uninitialized data.
int a; if (cond1) { a = 5; } else { if (cond2) { a = 10; } } use(a); do_other_stuff(); use(a);
Lets say that cond1 & cond2. Should both calls to use(a) be guaranteed to read the same value from uninitialized data?
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Of course they should see the same value. Holy cow you’re throwing the easiest examples at me. It’s like you’re making my point for me: that this is easy to fix but that some people need compiler educations.
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Okay, and that also means that using MADV_FREE in malloc and elsewhere is not possible either, which is a massive performance cost. Uninitialized memory can and does change value at runtime beyond just compiler optimizations avoiding saving uninitialized data via spill / restore.
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That's likely glibc what is going to be doing for their stack cache since MADV_DONTNEED is a significant performance cost for their implementation, and it doesn't become a non-issue if restricted to malloc since it still means that uninitialized memory can change between reads.
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Reading uninit data being undefined instead of locking it to an unspecified value permits massive optimizations like MADV_FREE and more efficient register allocation/spilling. Similarly, other memory safety issues being undefined permits optimization / freedom of implementation.
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MADV_FREE has nothing to do with rewriting code, or compiler optimizations, and yes it is certainly a massive optimization. Code that's reading uninitialized memory is undefined and dangerous. It doesn't make that substantially worse. It does make it act a bit weirder, sure.