[llvm] [PGO] Skip optimizing probes that don't fit. (PR #70875)

[Hongtao Yu via llvm-commits]

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@@ -324,6 +326,17 @@ void SampleProfileProber::instrumentOneFunc(Function &F, TargetMachine *TM) {
   for (auto &I : CallProbeIds) {
     auto *Call = I.first;
     uint32_t Index = I.second;
+
+    // There's a limit on the number of probe indices that can be optimized.
+    // The current implementation uses the lower 16 bits of the discriminator
+    // so anything larger than 0xFFFF will be ignored.
+    if (Index > 0xFFFF) {
+      std::string Msg = "Pseudo instrumentation incomplete for " +
+                        std::string(F.getName()) + " because it's too large";
+      Ctx.diagnose(DiagnosticInfoSampleProfile(M->getName().data(), Msg));
+      break;
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htyu wrote:

Since this is not processing in ID order, we should still be able to instrument for the rest callsites. Can we move the warning code out of the `for` loop?

https://github.com/llvm/llvm-project/pull/70875