Revert "[clang] Remove the DIFlagArgumentNotModified debug info flag"

This reverts commit rG1643734741d2 due to LLDB test failure.

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -18,6 +18,7 @@
 #include "CodeGenFunction.h"
 #include "CodeGenModule.h"
 #include "ConstantEmitter.h"
+#include "clang/Analysis/Analyses/ExprMutationAnalyzer.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/DeclFriend.h"
 #include "clang/AST/DeclObjC.h"
@@ -3685,6 +3686,15 @@ void CGDebugInfo::EmitFunctionStart(GlobalDecl GD, SourceLocation Loc,
   if (HasDecl && isa<FunctionDecl>(D))
     DeclCache[D->getCanonicalDecl()].reset(SP);
 
+  // We use the SPDefCache only in the case when the debug entry values option
+  // is set, in order to speed up parameters modification analysis.
+  //
+  // FIXME: Use AbstractCallee here to support ObjCMethodDecl.
+  if (CGM.getCodeGenOpts().EnableDebugEntryValues && HasDecl)
+    if (auto *FD = dyn_cast<FunctionDecl>(D))
+      if (FD->hasBody() && !FD->param_empty())
+        SPDefCache[FD].reset(SP);
+
   // Push the function onto the lexical block stack.
   LexicalBlockStack.emplace_back(SP);
 
@@ -4079,6 +4089,11 @@ llvm::DILocalVariable *CGDebugInfo::EmitDeclare(const VarDecl *VD,
                          llvm::DebugLoc::get(Line, Column, Scope, CurInlinedAt),
                          Builder.GetInsertBlock());
 
+  if (CGM.getCodeGenOpts().EnableDebugEntryValues && ArgNo) {
+    if (auto *PD = dyn_cast<ParmVarDecl>(VD))
+      ParamCache[PD].reset(D);
+  }
+
   return D;
 }
 
@@ -4694,6 +4709,29 @@ void CGDebugInfo::setDwoId(uint64_t Signature) {
   TheCU->setDWOId(Signature);
 }
 
+/// Analyzes each function parameter to determine whether it is constant
+/// throughout the function body.
+static void analyzeParametersModification(
+    ASTContext &Ctx,
+    llvm::DenseMap<const FunctionDecl *, llvm::TrackingMDRef> &SPDefCache,
+    llvm::DenseMap<const ParmVarDecl *, llvm::TrackingMDRef> &ParamCache) {
+  for (auto &SP : SPDefCache) {
+    auto *FD = SP.first;
+    assert(FD->hasBody() && "Functions must have body here");
+    const Stmt *FuncBody = (*FD).getBody();
+    for (auto Parm : FD->parameters()) {
+      ExprMutationAnalyzer FuncAnalyzer(*FuncBody, Ctx);
+      if (FuncAnalyzer.isMutated(Parm))
+        continue;
+
+      auto I = ParamCache.find(Parm);
+      assert(I != ParamCache.end() && "Parameters should be already cached");
+      auto *DIParm = cast<llvm::DILocalVariable>(I->second);
+      DIParm->setIsNotModified();
+    }
+  }
+}
+
 void CGDebugInfo::finalize() {
   // Creating types might create further types - invalidating the current
   // element and the size(), so don't cache/reference them.
@@ -4766,6 +4804,10 @@ void CGDebugInfo::finalize() {
     if (auto MD = TypeCache[RT])
       DBuilder.retainType(cast<llvm::DIType>(MD));
 
+  if (CGM.getCodeGenOpts().EnableDebugEntryValues)
+    // This will be used to emit debug entry values.
+    analyzeParametersModification(CGM.getContext(), SPDefCache, ParamCache);
+
   DBuilder.finalize();
 }
 

clang/lib/CodeGen/CGDebugInfo.h

@@ -146,6 +146,10 @@ class CGDebugInfo {
 
   llvm::DenseMap<const char *, llvm::TrackingMDRef> DIFileCache;
   llvm::DenseMap<const FunctionDecl *, llvm::TrackingMDRef> SPCache;
+  /// Cache function definitions relevant to use for parameters mutation
+  /// analysis.
+  llvm::DenseMap<const FunctionDecl *, llvm::TrackingMDRef> SPDefCache;
+  llvm::DenseMap<const ParmVarDecl *, llvm::TrackingMDRef> ParamCache;
   /// Cache declarations relevant to DW_TAG_imported_declarations (C++
   /// using declarations) that aren't covered by other more specific caches.
   llvm::DenseMap<const Decl *, llvm::TrackingMDRef> DeclCache;

clang/test/CodeGen/debug-info-param-modification.c

@@ -0,0 +1,25 @@
+// RUN: %clang -Xclang -femit-debug-entry-values -g -O2 -Xclang -disable-llvm-passes -S -target x86_64-none-linux-gnu -emit-llvm %s -o - | FileCheck %s -check-prefix=CHECK-ENTRY-VAL-OPT
+// RUN: %clang -Xclang -femit-debug-entry-values -g -O2 -Xclang -disable-llvm-passes -S -target arm-none-linux-gnu -emit-llvm %s -o - | FileCheck %s -check-prefix=CHECK-ENTRY-VAL-OPT
+// RUN: %clang -Xclang -femit-debug-entry-values -g -O2 -Xclang -disable-llvm-passes -S -target aarch64-none-linux-gnu -emit-llvm %s -o - | FileCheck %s -check-prefix=CHECK-ENTRY-VAL-OPT
+// RUN: %clang -Xclang -femit-debug-entry-values -g -O2 -Xclang -disable-llvm-passes -S -target armeb-none-linux-gnu -emit-llvm %s -o - | FileCheck %s -check-prefix=CHECK-ENTRY-VAL-OPT
+
+// CHECK-ENTRY-VAL-OPT: !DILocalVariable(name: "a", arg: 1, scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: {{.*}})
+// CHECK-ENTRY-VAL-OPT: !DILocalVariable(name: "b", arg: 2, scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: {{.*}}, flags: DIFlagArgumentNotModified)
+//
+// For the os_log_helper:
+// CHECK-ENTRY-VAL-OPT: !DILocalVariable(name: "buffer", arg: 1, {{.*}}, flags: DIFlagArtificial)
+//
+// RUN: %clang -g -O2 -Xclang -disable-llvm-passes -target x86_64-none-linux-gnu -S -emit-llvm %s -o - | FileCheck %s
+// CHECK-NOT: !DILocalVariable(name: "b", arg: 2, scope: {{.*}}, file: {{.*}}, line: {{.*}}, type: {{.*}}, flags: DIFlagArgumentNotModified)
+//
+// For the os_log_helper:
+// CHECK: !DILocalVariable(name: "buffer", arg: 1, {{.*}}, flags: DIFlagArtificial)
+
+int fn2 (int a, int b) {
+  ++a;
+  return b;
+}
+
+void test_builtin_os_log(void *buf, int i, const char *data) {
+  __builtin_os_log_format(buf, "%d %{public}s %{private}.16P", i, data, data);
+}