[PATCH] D132623: [CodeGen] Disable tail calls at -O0/-O1

[Arthur Eubanks via Phabricator via llvm-commits]

aeubanks added a comment.

In D132623#3775541 <https://reviews.llvm.org/D132623#3775541>, @jrtc27 wrote:

> In D132623#3775514 <https://reviews.llvm.org/D132623#3775514>, @aeubanks wrote:
>
>> The contract we have with the -O1 pipeline is to attempt to generate debuggable code as much as possible
>
> No it's not. What we say is:
>
>       :option:`-O0` Means "no optimization": this level compiles the fastest and
>       generates the most debuggable code.
>   
>       :option:`-O1` Somewhere between :option:`-O0` and :option:`-O2`.
>   
>       :option:`-O2` Moderate level of optimization which enables most
>       optimizations.
>   
>   ...
>   
>   
>       :option:`-Og` Like :option:`-O1`. In future versions, this option might
>       disable different optimizations in order to improve debuggability.

The -O1 pipeline has been tuned in the past to attempt to keep debuggability, and in OptimizationLevel.h <https://github.com/llvm/llvm-project/blob/178554f3c8f983bd192818b6d46e4d95560c4964/llvm/include/llvm/Passes/OptimizationLevel.h#L43> we say

  /// Optimize quickly without destroying debuggability.
  ///
  /// This level is tuned to produce a result from the optimizer as quickly
  /// as possible and to avoid destroying debuggability. This tends to result
  /// in a very good development mode where the compiled code will be
  /// immediately executed as part of testing. As a consequence, where
  /// possible, we would like to produce efficient-to-execute code, but not
  /// if it significantly slows down compilation or would prevent even basic
  /// debugging of the resulting binary.
  ///
  /// As an example, complex loop transformations such as versioning,
  /// vectorization, or fusion don't make sense here due to the degree to
  /// which the executed code differs from the source code, and the compile
  /// time cost.
  static const OptimizationLevel O1;
   

So I'd say that currently we do expect -O1 to generate debuggable code. If there's ever a push for a separate -Og pipeline that's fine, but we don't have that right now.


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