[llvm] [ctx_prof] Add Inlining support (PR #106154)

[Mircea Trofin via llvm-commits]

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@@ -2116,6 +2119,203 @@ inlineRetainOrClaimRVCalls(CallBase &CB, objcarc::ARCInstKind RVCallKind,
   }
 }
 
+// In contextual profiling, when an inline succeeds, we want to remap the
+// indices of the callee in the index space of the caller. We can't just leave
+// them as-is because the same callee may appear in other places in this caller
+// (other callsites), and its (callee's) counters and sub-contextual profile
+// tree would be potentially different.
+// Not all BBs of the callee may survive the opportunistic DCE InlineFunction
+// does (same goes for callsites in the callee).
+// We will return a pair of vectors, one for basic block IDs and one for
+// callsites. For such a vector V, V[Idx] will be -1 if the callee
+// instrumentation with index Idx did not survive inlining, and a new value
+// otherwise.
+// This function will update the instrumentation intrinsics accordingly,
+// mapping indices as described above. We also replace the "name" operand
+// because we use it to distinguish between "own" instrumentation and "from
+// callee" instrumentation when performing the traversal of the CFG of the
+// caller. We traverse depth-first from the callsite's BB and up to the point we
+// hit owned BBs.
+// The return values will be then used to update the contextual
+// profile. Note: we only update the "name" and "index" operands in the
+// instrumentation intrinsics, we leave the hash and total nr of indices as-is,
+// it's not worth updating those.
+static const std::pair<std::vector<int64_t>, std::vector<int64_t>>
+remapIndices(Function &Caller, BasicBlock *StartBB,
+             CtxProfAnalysis::Result &CtxProf, uint32_t CalleeCounters,
+             uint32_t CalleeCallsites) {
+  // We'll allocate a new ID to imported callsite counters and callsites. We're
+  // using -1 to indicate a counter we delete. Most likely the entry, for
+  // example, will be deleted - we don't want 2 IDs in the same BB, and the
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mtrofin wrote:

no :) the callee entry BB is cloned in the BB of the callsite. What the "deletion" is about is the ID - i.e. the instrumentation instruction (the "ID" is the index of the instrumentation instruction. It IDs the BB, basically) - and it's something `remapIndices` will likely do. It won't always do that: if the callsite BB didn't have an ID (because MST decided not to add instrumentation to that BB), then we have no reason to delete the instrumentation the callee entry BB comes with.

https://github.com/llvm/llvm-project/pull/106154