Rather than always creating a new local and storing the result of
a binary operation into said local, we now leave it on top of the stack.
This allows for better codegen as we need less instructions, as well
as less total amount of locals.
When a local is no longer needed (for instance, it was used as
a temporary during arithmetic), it can be appended to one of
the typed freelists. This allows us to re-use locals and therefore
require less locals, reducing the binary size, as well as runtime
initialization.
This effectively reverts 22690efcc2378222503cb8aaad26a6f4a539f5aa,
re-opening #11818.
This had the following problems:
* Buggy on some targets (macOS, Windows)
* Messy output to the terminal
These problems need to be solved before moving forward with this.
This is likely the cause of the flaky test failures in master branch.
Since we have some test coverage for incremental compilation, it's not
OK to leave proper memory management of Fn objects as "TODO".
This improves the following test case:
```zig
pub fn main() !void {
try foo();
}
fn foo() !void {
return error.Bad;
}
```
The error return trace now points to the `try` token instead of pointing
to the foo() function call, matching stage1.
Closes#12308.
Sema: insert an error return trace frame when appropriate when analyzing
ret_load. Also optimize the instructions to avoid an unnecessary block
sent to the backends.
AstGen: always emit a dbg_stmt for return expressions, in between the
defer instructions and the return instruction.
This improves the following test case:
```zig
pub fn main() !void {
return foo();
}
fn foo() !void {
return error.Bad;
}
```
The error return trace now points to the return token instead of
pointing to the foo() function call, matching stage1.
stage2 was adding bogus error return trace frames when an error was not
being returned. This commit makes several improvements:
* Make a runtime check if necessary to only emit a frame into the error
return trace when an actual error is returned.
* Use the `analyzeIsNonErrComptimeOnly` machinery to avoid runtime
checks when it is compile-time-known that the value is an error, or a
non-error.
* Make std.builtin.returnError take a non-optional stack trace pointer.
closes#12174
