[clang] Remove the DIFlagArgumentNotModified debug info flag

It turns out that the ExprMutationAnalyzer can be very slow when AST
gets huge in some cases. The idea is to move this analysis to the LLVM
back-end level (more precisely, in the LiveDebugValues pass). The new
approach will remove the performance regression, simplify the
implementation and give us front-end independent implementation.

Differential Revision: https://reviews.llvm.org/D68206

3 files changed, 0 insertions, 71 deletions

diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 75c4b2ae233..399fa95c3e0 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -18,7 +18,6 @@
 #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"
@@ -3686,15 +3685,6 @@ 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);
 
@@ -4089,11 +4079,6 @@ 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;
 }
 
@@ -4709,29 +4694,6 @@ 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.
@@ -4804,10 +4766,6 @@ 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();
 }
 
diff --git a/clang/lib/CodeGen/CGDebugInfo.h b/clang/lib/CodeGen/CGDebugInfo.h
index 9a097615b4b..5341bfa7f35 100644
--- a/clang/lib/CodeGen/CGDebugInfo.h
+++ b/clang/lib/CodeGen/CGDebugInfo.h
@@ -146,10 +146,6 @@ 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;
diff --git a/clang/test/CodeGen/debug-info-param-modification.c b/clang/test/CodeGen/debug-info-param-modification.c
deleted file mode 100644
index f0a13a3777d..00000000000
--- a/clang/test/CodeGen/debug-info-param-modification.c
+++ /dev/null
@@ -1,25 +0,0 @@
-// 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);
-}