[Transforms][IPO] Add remarks for ArgumentPromotion and DeadArgumentE… (#105740)

…limination

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:          'eliminating argument '
      - ArgName:         uattr.coerce0
      - String:          '('
      - ArgIndex:        '1'
      - 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 '
    - ArgName:         sk
    - String:          '('
    - ArgIndex:        '0'
    - String:          ')'
    - String:          ' to pass by value'
```
  [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)
+               << "eliminating argument " << ore::NV("ArgName", I->getName())
+               << "(" << ore::NV("ArgIndex", ArgNo) << ")";
+      });
+
       NewArgIndices.push_back((unsigned)-1);
     } else {
       const auto &ArgParts = ArgsToPromote.find(&*I)->second;
@@ -147,6 +155,13 @@ doPromotion(Function *F, FunctionAnalysisManager &FAM,
         ArgAttrVec.push_back(AttributeSet());
       }
       ++NumArgumentsPromoted;
+      ORE.emit([&]() {
+        return OptimizationRemark(DEBUG_TYPE, "ArgumentPromoted", F)
+               << "promoting argument " << ore::NV("ArgName", I->getName())
+               << "(" << ore::NV("ArgIndex", ArgNo) << ")"
+               << " to pass by value";
+      });
+
       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)
+               << "eliminating argument " << ore::NV("ArgName", I->getName())
+               << "(" << ore::NV("ArgIndex", ArgI) << ")";
+      });
       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");

llvm/test/Transforms/ArgumentPromotion/2008-02-01-ReturnAttrs.ll

@@ -1,12 +1,22 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --function-signature --scrub-attributes
-; RUN: opt < %s -passes=argpromotion -S | FileCheck %s
+; RUN: opt < %s -passes=argpromotion -S -pass-remarks-output=%t | FileCheck %s
+; RUN: cat %t | FileCheck -check-prefix=REMARK %s
 
 define internal i32 @deref(ptr %x) nounwind {
 ; CHECK-LABEL: define {{[^@]+}}@deref
 ; CHECK-SAME: (i32 [[X_0_VAL:%.*]]) #[[ATTR0:[0-9]+]] {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    ret i32 [[X_0_VAL]]
 ;
+; REMARK-LABEL: Function: deref
+; REMARK:       Args:
+; REMARK-NEXT:    - String:   'promoting argument '
+; REMARK-NEXT:    - ArgName:  x
+; REMARK-NEXT:    - String:   '('
+; REMARK-NEXT:    - ArgIndex: '0'
+; REMARK-NEXT:    - String:   ')'
+; REMARK-NEXT:    - String:   ' to pass by value'
+;
 entry:
   %temp2 = load i32, ptr %x, align 4
   ret i32 %temp2

llvm/test/Transforms/DeadArgElim/2007-12-20-ParamAttrs.ll

@@ -1,10 +1,19 @@
-; RUN: opt < %s -passes=deadargelim -S | FileCheck %s
+; RUN: opt < %s -passes=deadargelim -S -pass-remarks-output=%t | FileCheck %s
+; RUN: cat %t | FileCheck -check-prefix=REMARK %s
 
 %struct = type { }
 
 @g = global i8 0
 
 ; CHECK: define internal void @foo(i8 signext %y) [[NUW:#[0-9]+]]
+;
+; REMARK-LABEL: Function: foo
+; REMARK:       Args:
+; REMARK-NEXT:    - String:   'eliminating argument '
+; REMARK-NEXT:    - ArgName:  p
+; REMARK-NEXT:    - String:   '('
+; REMARK-NEXT:    - ArgIndex: '0'
+; REMARK-NEXT:    - String:   ')'
 
 define internal zeroext i8 @foo(ptr inreg %p, i8 signext %y, ... )  nounwind {
   store i8 %y, ptr @g