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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: None (yonghong-song)

<details>
<summary>Changes</summary>

…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:
    - Function:        mptcp_check_data_fin
      DebugLoc:        { File: 'bpf-next/net/mptcp/protocol.c', Line: 572,
                         Column: 0 }
    - 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:
    - Function:        map_delete_elem
      DebugLoc:        { File: 'bpf-next/kernel/bpf/syscall.c', Line: 1670,
                         Column: 0 }
    - 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:
    - Function:        mptcp_subflow_ctx
      DebugLoc:        { File: 'bpf-next/net/mptcp/protocol.h', Line: 570,
                         Column: 0 }
    - String:          ' promoting argument '
    - String:          '0'
    - String:          ' ('
    - String:          sk
    - String:          ')'
```
  [1] https://github.com/llvm/llvm-project/issues/104678

---
Full diff: https://github.com/llvm/llvm-project/pull/105740.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/IPO/ArgumentPromotion.cpp (+14) 
- (modified) llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp (+14) 


``````````diff
diff --git a/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp b/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
index 452fff7898d0ea..9369d2be74bb7d 100644
--- a/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
+++ b/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)
+               << ore::NV("Function", 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)
+               << ore::NV("Function", F) << " promoting argument "
+               << std::to_string(ArgNo) << " (" << I->getName() << ")";
+      });
+
       NewArgIndices.push_back((unsigned)-1);
       NewArgNo += ArgParts.size();
     }
diff --git a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp b/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
index f5a7ab26a49e96..bb71993995cf18 100644
--- a/llvm/lib/Transforms/IPO/DeadArgumentElimination.cpp
+++ b/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)
+               << ore::NV("Function", F) << " removing argument "
+               << std::to_string(ArgI) << " (" << I->getName() << ")";
+      });
       LLVM_DEBUG(dbgs() << "DeadArgumentEliminationPass - Removing argument "
                         << ArgI << " (" << I->getName() << ") from "
                         << F->getName() << "\n");
@@ -810,6 +818,12 @@ bool DeadArgumentEliminationPass::removeDeadStuffFromFunction(Function *F) {
         NewRetIdxs[Ri] = RetTypes.size() - 1;
       } else {
         ++NumRetValsEliminated;
+
+        ORE.emit([&]() {
+          return OptimizationRemark(DEBUG_TYPE, "ReturnValueRemoved", F)
+                 << ore::NV("Function", F) << " removing return value "
+                 << std::to_string(Ri);
+        });
         LLVM_DEBUG(
             dbgs() << "DeadArgumentEliminationPass - Removing return value "
                    << Ri << " from " << F->getName() << "\n");

``````````

</details>


https://github.com/llvm/llvm-project/pull/105740