Auto merge of #120368 - klensy:llvm-fixme, r=nikic

llvm-wrapper: remove llvm 12 hack

effectively reverts 9a8acea

r? `@nikic`

compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp

@@ -934,25 +934,16 @@ LLVMRustOptimize(
     } else {
       for (const auto &C : PipelineStartEPCallbacks)
         PB.registerPipelineStartEPCallback(C);
-      if (OptStage != LLVMRustOptStage::PreLinkThinLTO) {
-        for (const auto &C : OptimizerLastEPCallbacks)
-          PB.registerOptimizerLastEPCallback(C);
-      }
+      for (const auto &C : OptimizerLastEPCallbacks)
+        PB.registerOptimizerLastEPCallback(C);
 
       switch (OptStage) {
       case LLVMRustOptStage::PreLinkNoLTO:
         MPM = PB.buildPerModuleDefaultPipeline(OptLevel, DebugPassManager);
         break;
       case LLVMRustOptStage::PreLinkThinLTO:
         MPM = PB.buildThinLTOPreLinkDefaultPipeline(OptLevel);
-        // The ThinLTOPreLink pipeline already includes ThinLTOBuffer passes. However, callback
-        // passes may still run afterwards. This means we need to run the buffer passes again.
-        // FIXME: In LLVM 13, the ThinLTOPreLink pipeline also runs OptimizerLastEPCallbacks
-        // before the RequiredLTOPreLinkPasses, in which case we can remove these hacks.
-        if (OptimizerLastEPCallbacks.empty())
-          NeedThinLTOBufferPasses = false;
-        for (const auto &C : OptimizerLastEPCallbacks)
-          C(MPM, OptLevel);
+        NeedThinLTOBufferPasses = false;
         break;
       case LLVMRustOptStage::PreLinkFatLTO:
         MPM = PB.buildLTOPreLinkDefaultPipeline(OptLevel);