This change introduces a new clang switch -fpseudo-probe-for-profiling to enable AutoFDO with pseudo instrumentation. Please refer to https://reviews.llvm.org/D86193 for the whole story.
One implication from pseudo-probe instrumentation is that the profile is now sensitive to CFG changes. We perform the pseudo instrumentation very early in the pre-LTO pipeline, before any CFG transformation. This ensures that the CFG instrumented and annotated is stable and optimization-resilient.
The early instrumentation also allows the inliner to duplicate probes for inlined instances. When a probe along with the other instructions of a callee function are inlined into its caller function, the GUID of the callee function goes with the probe. This allows samples collected on inlined probes to be reported for the original callee function.