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Make sure that compiler and linker don't optimize the section's contents away by adding the global holding the data to "llvm.used". The volatile load in the main shim is retained because "llvm.used", which translates to SHF_GNU_RETAIN on ELF targets, requires a reasonably recent linker; emitting the volatile load ensures compatibility with older linkers, at least when libstd is used. Pretty printers in dylib dependencies are now emitted by the main crate instead of the dylib; apart from matching how rlibs are handled, this approach has the advantage that `omit_gdb_pretty_printer_section` keeps working with dylib dependencies.
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