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

[Hongtao Yu via llvm-commits]

================
@@ -221,12 +222,26 @@ void SampleProfileProber::computeProbeIdForBlocks() {
 }
 
 void SampleProfileProber::computeProbeIdForCallsites() {
+  LLVMContext &Ctx = F->getContext();
+  Module *M = F->getParent();
+
   for (auto &BB : *F) {
     for (auto &I : BB) {
       if (!isa<CallBase>(I))
         continue;
       if (isa<IntrinsicInst>(&I))
         continue;
+
+      // 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 (LastProbeId >= 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;
----------------
htyu wrote:

This doesn't break the outer loop. Maybe just return?

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