[clang] [clang] Add optional pass to remove UBSAN traps using PGO (PR #84214)

[Vitaly Buka via cfe-commits]

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@@ -744,6 +750,21 @@ static void addSanitizers(const Triple &TargetTriple,
     // LastEP does not need GlobalsAA.
     PB.registerOptimizerLastEPCallback(SanitizersCallback);
   }
+
+  if (ClRemoveTraps) {
+    // We can optimize after inliner, and PGO profile matching. The hook below
+    // is called from `buildModuleOptimizationPipeline` just after profile use,
+    // and inliner is a part of `buildModuleSimplificationPipeline`, which is
+    // before `buildModuleOptimizationPipeline`.
+    PB.registerOptimizerEarlyEPCallback([&](ModulePassManager &MPM,
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vitalybuka wrote:

It's bisected to SimplifyCFG , the one after ScalarOptimizerLateEPCallback.
Most trap blocks preceded by empty blocks with unconditional branch as terminator. And they are always cold.
Inserting `SimplifyCFGPass` solves the issue and now I see no regression.


https://github.com/llvm/llvm-project/pull/84214