[CodeGen][NPM] Do not implicitly flush pipeline when switching to CGSCC (#173315)

Author: boomanaiden154

llvm/include/llvm/Passes/CodeGenPassBuilder.h

@@ -277,12 +277,17 @@ template <typename DerivedT, typename TargetMachineT> class CodeGenPassBuilder {
 
   void requireCGSCCOrder(PassManagerWrapper &PMW) const {
     assert(!AddInCGSCCOrder);
-    flushFPMsToMPM(PMW);
+    assert(PMW.FPM.isEmpty() && PMW.MFPM.isEmpty() &&
+           "Requiring CGSCC ordering requires flushing the current function "
+           "pipelines to the MPM.");
     AddInCGSCCOrder = true;
   }
+
   void stopAddingInCGSCCOrder(PassManagerWrapper &PMW) const {
     assert(AddInCGSCCOrder);
-    flushFPMsToMPM(PMW);
+    assert(PMW.FPM.isEmpty() && PMW.MFPM.isEmpty() &&
+           "Stopping CGSCC ordering requires flushing the current function "
+           "pipelines to the MPM.");
     AddInCGSCCOrder = false;
   }
 

llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp

@@ -2206,6 +2206,7 @@ void AMDGPUCodeGenPassBuilder::addCodeGenPrepare(
   // many cases.
   flushFPMsToMPM(PMW);
   addModulePass(AMDGPULowerBufferFatPointersPass(TM), PMW);
+  flushFPMsToMPM(PMW);
   requireCGSCCOrder(PMW);
 
   addModulePass(AMDGPULowerIntrinsicsPass(TM), PMW);