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Affirm `-Cforce-frame-pointers=off` does not override This PR exists to document that we (that is, the compiler reviewer) implicitly made a decision in rust-lang/rust#86652 that defies the expectations of some programmers. Some programmers believe `-Cforce-frame-pointers=false` should obey the programmer in all cases, forcing the compiler to avoid generating frame pointers, even if the target specification would indicate they must be generated. However, many targets rely on frame pointers for fast or sound unwinding. T-compiler had a weekly triage meeting on 2025-05-22. This topic was put to discussion because some programmers may expect the target-overriding behavior. In that meeting we decided removing frame pointers, at least with regards to the contract of the `-Cforce-frame-pointers` option, is not required, even if `=off` is passed, and that we will not do so if the target would expect them. This follows from the documentation here: https://doc.rust-lang.org/rustc/codegen-options/index.html#force-frame-pointers We may separately pursue trying to clarify the situation more emphatically in our documentation, or warn when people pass the option when it doesn't do anything.
The files here use the LLVM FileCheck framework, documented at https://llvm.org/docs/CommandGuide/FileCheck.html.
One extension worth noting is the use of revisions as custom prefixes for FileCheck. If your codegen test has different behavior based on the chosen target or different compiler flags that you want to exercise, you can use a revisions annotation, like so:
// revisions: aaa bbb
// [bbb] compile-flags: --flags-for-bbb
After specifying those variations, you can write different expected, or
explicitly unexpected output by using <prefix>-SAME: and <prefix>-NOT:,
like so:
// CHECK: expected code
// aaa-SAME: emitted-only-for-aaa
// aaa-NOT: emitted-only-for-bbb
// bbb-NOT: emitted-only-for-aaa
// bbb-SAME: emitted-only-for-bbb