[Transforms][IPO] Add remarks for ArgumentPromotion and DeadArgumentElimination

ArgumentPromotion and DeadArgumentElimination passes may change
function signature. This makes bpf tracing difficult since
users either not aware of signature change or need to poke
into IR or assembly to understand the function signature change.

This patch enabled to emit some remarks so if recompiling
with -foptimization-record-file=<file>, users can check remarks
to see what kind of signature changes for a particular function.
The following are some examples for implemented remarks:

  Pass:            deadargelim
  Name:            ReturnValueRemoved
  DebugLoc:        { File: 'bpf-next/net/mptcp/protocol.c', Line: 572, Column: 0 }
  Function:        mptcp_check_data_fin
  Args:
    - String:          'removing return value '
    - String:          '0'

  Pass:            deadargelim
  Name:            ArgumentRemoved
  DebugLoc:        { File: 'bpf-next/kernel/bpf/syscall.c', Line: 1670, Column: 0 }
  Function:        map_delete_elem
  Args:
    - String:          'removing argument '
    - String:          '1'
    - String:          ' ('
    - String:          uattr.coerce0
    - String:          ')'

  Pass:            argpromotion
  Name:            ArgumentPromoted
  DebugLoc:        { File: 'bpf-next/net/mptcp/protocol.h', Line: 570, Column: 0 }
  Function:        mptcp_subflow_ctx
  Args:
    - String:          'promoting argument '
    - String:          '0'
    - String:          ' ('
    - String:          sk
    - String:          ')'

  [1] #104678

Author: Yonghong Song

llvm/lib/Transforms/IPO/ArgumentPromotion.cpp

@@ -42,6 +42,7 @@
 #include "llvm/Analysis/CallGraph.h"
 #include "llvm/Analysis/Loads.h"
 #include "llvm/Analysis/MemoryLocation.h"
+#include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/Argument.h"
@@ -126,6 +127,7 @@ doPromotion(Function *F, FunctionAnalysisManager &FAM,
   // arguments.
   SmallVector<unsigned> NewArgIndices;
   AttributeList PAL = F->getAttributes();
+  OptimizationRemarkEmitter ORE(F);
 
   // First, determine the new argument list
   unsigned ArgNo = 0, NewArgNo = 0;
@@ -139,6 +141,12 @@ doPromotion(Function *F, FunctionAnalysisManager &FAM,
     } else if (I->use_empty()) {
       // Dead argument (which are always marked as promotable)
       ++NumArgumentsDead;
+      ORE.emit([&]() {
+        return OptimizationRemark(DEBUG_TYPE, "ArgumentRemoved", F)
+               << "removing argument " << std::to_string(ArgNo) << " ("
+               << I->getName() << ")";
+      });
+
       NewArgIndices.push_back((unsigned)-1);
     } else {
       const auto &ArgParts = ArgsToPromote.find(&*I)->second;
@@ -147,6 +155,12 @@ doPromotion(Function *F, FunctionAnalysisManager &FAM,
         ArgAttrVec.push_back(AttributeSet());
       }
       ++NumArgumentsPromoted;
+      ORE.emit([&]() {
+        return OptimizationRemark(DEBUG_TYPE, "ArgumentPromoted", F)
+               << "promoting argument " << std::to_string(ArgNo) << " ("
+               << I->getName() << ")";
+      });
+
       NewArgIndices.push_back((unsigned)-1);
       NewArgNo += ArgParts.size();
     }

llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp

@@ -19,6 +19,7 @@
 #include "llvm/Transforms/IPO/DeadArgumentElimination.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/IR/Argument.h"
 #include "llvm/IR/AttributeMask.h"
 #include "llvm/IR/Attributes.h"
@@ -748,6 +749,7 @@ bool DeadArgumentEliminationPass::removeDeadStuffFromFunction(Function *F) {
   // Set up to build a new list of parameter attributes.
   SmallVector<AttributeSet, 8> ArgAttrVec;
   const AttributeList &PAL = F->getAttributes();
+  OptimizationRemarkEmitter ORE(F);
 
   // Remember which arguments are still alive.
   SmallVector<bool, 10> ArgAlive(FTy->getNumParams(), false);
@@ -765,6 +767,12 @@ bool DeadArgumentEliminationPass::removeDeadStuffFromFunction(Function *F) {
       HasLiveReturnedArg |= PAL.hasParamAttr(ArgI, Attribute::Returned);
     } else {
       ++NumArgumentsEliminated;
+
+      ORE.emit([&]() {
+        return OptimizationRemark(DEBUG_TYPE, "ArgumentRemoved", F)
+               << "removing argument " << std::to_string(ArgI) << " ("
+               << I->getName() << ")";
+      });
       LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - Removing argument "
                         << ArgI << " (" << I->getName() << ") from "
                         << F->getName() << "\n");
@@ -810,6 +818,11 @@ bool DeadArgumentEliminationPass::removeDeadStuffFromFunction(Function *F) {
         NewRetIdxs[Ri] = RetTypes.size() - 1;
       } else {
         ++NumRetValsEliminated;
+
+        ORE.emit([&]() {
+          return OptimizationRemark(DEBUG_TYPE, "ReturnValueRemoved", F)
+                 << "removing return value " << std::to_string(Ri);
+        });
         LLVM_DEBUG(
             dbgs() << "DeadArgumentEliminationPass - Removing return value "
                    << Ri << " from " << F->getName() << "\n");