[UBSAN] Emit optimization remarks (#88304)

Author: vitalybuka

llvm/lib/IR/DiagnosticInfo.cpp

@@ -179,8 +179,12 @@ DiagnosticInfoOptimizationBase::Argument::Argument(StringRef Key,
   else if (isa<Constant>(V)) {
     raw_string_ostream OS(Val);
     V->printAsOperand(OS, /*PrintType=*/false);
-  } else if (auto *I = dyn_cast<Instruction>(V))
+  } else if (auto *I = dyn_cast<Instruction>(V)) {
     Val = I->getOpcodeName();
+  } else if (auto *MD = dyn_cast<MetadataAsValue>(V)) {
+    if (auto *S = dyn_cast<MDString>(MD->getMetadata()))
+      Val = S->getString();
+  }
 }
 
 DiagnosticInfoOptimizationBase::Argument::Argument(StringRef Key, const Type *T)

llvm/lib/Transforms/Instrumentation/LowerAllowCheckPass.cpp

@@ -10,11 +10,16 @@
 
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/Analysis/ProfileSummaryInfo.h"
 #include "llvm/IR/Constant.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Metadata.h"
 #include "llvm/Support/RandomNumberGenerator.h"
 #include <memory>
 #include <random>
@@ -35,13 +40,41 @@ static cl::opt<float>
 STATISTIC(NumChecksTotal, "Number of checks");
 STATISTIC(NumChecksRemoved, "Number of removed checks");
 
+struct RemarkInfo {
+  ore::NV Kind;
+  ore::NV F;
+  ore::NV BB;
+  explicit RemarkInfo(IntrinsicInst *II)
+      : Kind("Kind", II->getArgOperand(0)),
+        F("Function", II->getParent()->getParent()),
+        BB("Block", II->getParent()->getName()) {}
+};
+
+static void emitRemark(IntrinsicInst *II, OptimizationRemarkEmitter &ORE,
+                       bool Removed) {
+  if (Removed) {
+    ORE.emit([&]() {
+      RemarkInfo Info(II);
+      return OptimizationRemark(DEBUG_TYPE, "Removed", II)
+             << "Removed check: Kind=" << Info.Kind << " F=" << Info.F
+             << " BB=" << Info.BB;
+    });
+  } else {
+    ORE.emit([&]() {
+      RemarkInfo Info(II);
+      return OptimizationRemarkMissed(DEBUG_TYPE, "Allowed", II)
+             << "Allowed check: Kind=" << Info.Kind << " F=" << Info.F
+             << " BB=" << Info.BB;
+    });
+  }
+}
+
 static bool removeUbsanTraps(Function &F, const BlockFrequencyInfo &BFI,
-                             const ProfileSummaryInfo *PSI) {
+                             const ProfileSummaryInfo *PSI,
+                             OptimizationRemarkEmitter &ORE) {
   SmallVector<std::pair<IntrinsicInst *, bool>, 16> ReplaceWithValue;
   std::unique_ptr<RandomNumberGenerator> Rng;
 
-  // TODO:
-  // https://github.com/llvm/llvm-project/pull/84858#discussion_r1520603139
   auto ShouldRemove = [&](bool IsHot) {
     if (!RandomRate.getNumOccurrences())
       return IsHot;
@@ -75,6 +108,7 @@ static bool removeUbsanTraps(Function &F, const BlockFrequencyInfo &BFI,
         });
         if (ToRemove)
           ++NumChecksRemoved;
+        emitRemark(II, ORE, ToRemove);
         break;
       }
       default:
@@ -99,9 +133,11 @@ PreservedAnalyses LowerAllowCheckPass::run(Function &F,
   ProfileSummaryInfo *PSI =
       MAMProxy.getCachedResult<ProfileSummaryAnalysis>(*F.getParent());
   BlockFrequencyInfo &BFI = AM.getResult<BlockFrequencyAnalysis>(F);
+  OptimizationRemarkEmitter &ORE =
+      AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
 
-  return removeUbsanTraps(F, BFI, PSI) ? PreservedAnalyses::none()
-                                       : PreservedAnalyses::all();
+  return removeUbsanTraps(F, BFI, PSI, ORE) ? PreservedAnalyses::none()
+                                            : PreservedAnalyses::all();
 }
 
 bool LowerAllowCheckPass::IsRequested() {

llvm/test/Transforms/lower-builtin-allow-check-remarks.ll

@@ -0,0 +1,24 @@
+; RUN: opt < %s -passes='require<profile-summary>,function(lower-allow-check)' -lower-allow-check-random-rate=1 -pass-remarks=lower-allow-check -pass-remarks-missed=lower-allow-check -S 2>&1 | FileCheck %s
+; RUN: opt < %s -passes='require<profile-summary>,function(lower-allow-check)' -lower-allow-check-random-rate=0 -pass-remarks=lower-allow-check -pass-remarks-missed=lower-allow-check -S 2>&1 | FileCheck %s --check-prefixes=REMOVE
+
+; CHECK: remark: <unknown>:0:0: Allowed check: Kind=test_check F=test_runtime BB=entry1
+; CHECK: remark: <unknown>:0:0: Allowed check: Kind=7 F=test_ubsan BB=entry2
+
+; REMOVE: remark: <unknown>:0:0: Removed check: Kind=test_check F=test_runtime BB=entry1
+; REMOVE: remark: <unknown>:0:0: Removed check: Kind=7 F=test_ubsan BB=entry2
+
+target triple = "x86_64-pc-linux-gnu"
+
+define i1 @test_runtime() local_unnamed_addr {
+entry1:
+  %allow = call i1 @llvm.allow.runtime.check(metadata !"test_check")
+  ret i1 %allow
+}
+
+declare i1 @llvm.allow.runtime.check(metadata) nounwind
+
+define i1 @test_ubsan() local_unnamed_addr {
+entry2:
+  %allow = call i1 @llvm.allow.ubsan.check(i8 7)
+  ret i1 %allow
+}