[clang] [llvm] [Clang]: Enable speculative devirtualization (PR #159685)

[Florian Hahn via llvm-commits]

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@@ -1641,6 +1642,24 @@ PassBuilder::buildModuleOptimizationPipeline(OptimizationLevel Level,
   if (!LTOPreLink)
     MPM.addPass(RelLookupTableConverterPass());
 
+  if (PTO.DevirtualizeSpeculatively && LTOPhase == ThinOrFullLTOPhase::None) {
+    MPM.addPass(WholeProgramDevirtPass(
+        /*ExportSummary*/ nullptr,
+        /*ImportSummary*/ nullptr,
+        /*DevirtSpeculatively*/ PTO.DevirtualizeSpeculatively));
+    MPM.addPass(LowerTypeTestsPass(nullptr, nullptr,
+                                   lowertypetests::DropTestKind::Assume));
+    if (EnableModuleInliner) {
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fhahn wrote:

You can add a phase odering test. Did you evaluate the compile-time impact of running the inliner again? Did you measure the perf impact of just running the inliner again, without `WholeProgramDevirtPass`?

https://github.com/llvm/llvm-project/pull/159685