[RFC] Emit dwarf data for signature-changed or new functions

llvm/include/llvm/Transforms/Utils/EmitChangedFuncDebugInfo.h

@@ -0,0 +1,33 @@
+//===- EmitChangedFuncDebugInfo.h - Emit Additional Debug Info -*- C++ --*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file
+/// Emit debug info for changed or new funcs.
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_EMITCHANGEDFUNCDEBUGINFO_H
+#define LLVM_TRANSFORMS_UTILS_EMITCHANGEDFUNCDEBUGINFO_H
+
+#include "llvm/IR/PassManager.h"
+
+namespace llvm {
+
+class Module;
+
+// Pass that emits late dwarf.
+class EmitChangedFuncDebugInfoPass
+    : public PassInfoMixin<EmitChangedFuncDebugInfoPass> {
+public:
+  EmitChangedFuncDebugInfoPass() = default;
+
+  PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM);
+};
+
+} // end namespace llvm
+
+#endif // LLVM_TRANSFORMS_UTILS_EMITCHANGEDFUNCDEBUGINFO_H

llvm/lib/Passes/PassBuilder.cpp

@@ -351,6 +351,7 @@
 #include "llvm/Transforms/Utils/DXILUpgrade.h"
 #include "llvm/Transforms/Utils/Debugify.h"
 #include "llvm/Transforms/Utils/DeclareRuntimeLibcalls.h"
+#include "llvm/Transforms/Utils/EmitChangedFuncDebugInfo.h"
 #include "llvm/Transforms/Utils/EntryExitInstrumenter.h"
 #include "llvm/Transforms/Utils/FixIrreducible.h"
 #include "llvm/Transforms/Utils/HelloWorld.h"

llvm/lib/Passes/PassBuilderPipelines.cpp

@@ -135,6 +135,7 @@
 #include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
 #include "llvm/Transforms/Utils/CanonicalizeAliases.h"
 #include "llvm/Transforms/Utils/CountVisits.h"
+#include "llvm/Transforms/Utils/EmitChangedFuncDebugInfo.h"
 #include "llvm/Transforms/Utils/EntryExitInstrumenter.h"
 #include "llvm/Transforms/Utils/ExtraPassManager.h"
 #include "llvm/Transforms/Utils/InjectTLIMappings.h"
@@ -1643,9 +1644,12 @@ PassBuilder::buildModuleOptimizationPipeline(OptimizationLevel Level,
   if (PTO.CallGraphProfile && !LTOPreLink)
     MPM.addPass(CGProfilePass(isLTOPostLink(LTOPhase)));
 
-  // RelLookupTableConverterPass runs later in LTO post-link pipeline.
-  if (!LTOPreLink)
+  // RelLookupTableConverterPass and EmitChangedFuncDebugInfoPass run later in
+  // LTO post-link pipeline.
+  if (!LTOPreLink) {
     MPM.addPass(RelLookupTableConverterPass());
+    MPM.addPass(EmitChangedFuncDebugInfoPass());
+  }
 
   return MPM;
 }

llvm/lib/Passes/PassRegistry.def

@@ -75,6 +75,7 @@ MODULE_PASS("dfsan", DataFlowSanitizerPass())
 MODULE_PASS("dot-callgraph", CallGraphDOTPrinterPass())
 MODULE_PASS("dxil-upgrade", DXILUpgradePass())
 MODULE_PASS("elim-avail-extern", EliminateAvailableExternallyPass())
+MODULE_PASS("emit-changed-func-debuginfo", EmitChangedFuncDebugInfoPass())
 MODULE_PASS("extract-blocks", BlockExtractorPass({}, false))
 MODULE_PASS("expand-variadics",
             ExpandVariadicsPass(ExpandVariadicsMode::Disable))

llvm/lib/Transforms/IPO/ArgumentPromotion.cpp

@@ -50,6 +50,7 @@
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/DIBuilder.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Dominators.h"
@@ -432,6 +433,16 @@ doPromotion(Function *F, FunctionAnalysisManager &FAM,
     PromoteMemToReg(Allocas, DT, &AC);
   }
 
+  // If argument(s) are dead (hence removed) or promoted, probably the function
+  // does not follow standard calling convention anymore. Add DW_CC_nocall to
+  // DISubroutineType to inform debugger that it may not be safe to call this
+  // function.
+  DISubprogram *SP = NF->getSubprogram();
+  if (SP) {
+    auto Temp = SP->getType()->cloneWithCC(llvm::dwarf::DW_CC_nocall);
+    SP->replaceType(MDNode::replaceWithPermanent(std::move(Temp)));
+  }
+
   return NF;
 }
 

llvm/lib/Transforms/Utils/CMakeLists.txt

@@ -23,6 +23,7 @@ add_llvm_component_library(LLVMTransformUtils
   DebugSSAUpdater.cpp
   DeclareRuntimeLibcalls.cpp
   DemoteRegToStack.cpp
+  EmitChangedFuncDebugInfo.cpp
   DXILUpgrade.cpp
   EntryExitInstrumenter.cpp
   EscapeEnumerator.cpp