Switch to using -debug-info-kind=constructor as default (from =limited)

Summary:
-debug-info-kind=constructor reduces the amount of class debug info that
is emitted; this patch switches to using this as the default.

Constructor homing emits the complete type info for a class only when the
constructor is emitted, so it is expected that there will be some classes that
are not defined in the debug info anymore because they are never constructed,
and we shouldn't need debug info for these classes.

I compared the PDB files for clang, and there are 273 class types that are defined with `=limited`
but not with `=constructor` (out of ~60,000 total class types).
We've looked at a number of the types that are no longer defined with =constructor. The vast
majority of cases are something like class A is used as a parameter in a member function of
some other class B, which is emitted. But the function that uses class A is never called, and class A
is never constructed, and therefore isn't emitted in the debug info.

Bug: https://bugs.llvm.org/show_bug.cgi?id=46537

Subscribers: aprantl, cfe-commits, lldb-commits

Tags: #clang, #lldb

Differential Revision: https://reviews.llvm.org/D79147

Author: amykhuang

clang/lib/Driver/ToolChains/Clang.cpp

@@ -498,7 +498,7 @@ static codegenoptions::DebugInfoKind DebugLevelToInfoKind(const Arg &A) {
     return codegenoptions::DebugLineTablesOnly;
   if (A.getOption().matches(options::OPT_gline_directives_only))
     return codegenoptions::DebugDirectivesOnly;
-  return codegenoptions::LimitedDebugInfo;
+  return codegenoptions::DebugInfoConstructor;
 }
 
 static bool mustUseNonLeafFramePointerForTarget(const llvm::Triple &Triple) {
@@ -2380,7 +2380,7 @@ static void CollectArgsForIntegratedAssembler(Compilation &C,
           CmdArgs.push_back(Value.data());
         } else {
           RenderDebugEnablingArgs(Args, CmdArgs,
-                                  codegenoptions::LimitedDebugInfo,
+                                  codegenoptions::DebugInfoConstructor,
                                   DwarfVersion, llvm::DebuggerKind::Default);
         }
       } else if (Value.startswith("-mcpu") || Value.startswith("-mfpu") ||
@@ -3653,7 +3653,7 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D,
   if (const Arg *A =
           Args.getLastArg(options::OPT_g_Group, options::OPT_gsplit_dwarf,
                           options::OPT_gsplit_dwarf_EQ)) {
-    DebugInfoKind = codegenoptions::LimitedDebugInfo;
+    DebugInfoKind = codegenoptions::DebugInfoConstructor;
 
     // If the last option explicitly specified a debug-info level, use it.
     if (checkDebugInfoOption(A, Args, D, TC) &&
@@ -3758,7 +3758,7 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D,
     if (checkDebugInfoOption(A, Args, D, TC)) {
       if (DebugInfoKind != codegenoptions::DebugLineTablesOnly &&
           DebugInfoKind != codegenoptions::DebugDirectivesOnly) {
-        DebugInfoKind = codegenoptions::LimitedDebugInfo;
+        DebugInfoKind = codegenoptions::DebugInfoConstructor;
         CmdArgs.push_back("-dwarf-ext-refs");
         CmdArgs.push_back("-fmodule-format=obj");
       }
@@ -3778,7 +3778,9 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D,
           TC.GetDefaultStandaloneDebug());
   if (const Arg *A = Args.getLastArg(options::OPT_fstandalone_debug))
     (void)checkDebugInfoOption(A, Args, D, TC);
-  if (DebugInfoKind == codegenoptions::LimitedDebugInfo && NeedFullDebug)
+  if ((DebugInfoKind == codegenoptions::LimitedDebugInfo ||
+       DebugInfoKind == codegenoptions::DebugInfoConstructor) &&
+      NeedFullDebug)
     DebugInfoKind = codegenoptions::FullDebugInfo;
 
   if (Args.hasFlag(options::OPT_gembed_source, options::OPT_gno_embed_source,
@@ -6552,7 +6554,7 @@ void Clang::AddClangCLArgs(const ArgList &Args, types::ID InputType,
                           options::OPT_gline_tables_only)) {
     *EmitCodeView = true;
     if (DebugInfoArg->getOption().matches(options::OPT__SLASH_Z7))
-      *DebugInfoKind = codegenoptions::LimitedDebugInfo;
+      *DebugInfoKind = codegenoptions::DebugInfoConstructor;
     else
       *DebugInfoKind = codegenoptions::DebugLineTablesOnly;
   } else {
@@ -6849,7 +6851,7 @@ void ClangAs::ConstructJob(Compilation &C, const JobAction &JA,
     // the guard for source type, however there is a test which asserts
     // that some assembler invocation receives no -debug-info-kind,
     // and it's not clear whether that test is just overly restrictive.
-    DebugInfoKind = (WantDebug ? codegenoptions::LimitedDebugInfo
+    DebugInfoKind = (WantDebug ? codegenoptions::DebugInfoConstructor
                                : codegenoptions::NoDebugInfo);
     // Add the -fdebug-compilation-dir flag if needed.
     addDebugCompDirArg(Args, CmdArgs, C.getDriver().getVFS());

clang/test/Driver/cl-options.c

@@ -524,11 +524,11 @@
 
 // RUN: %clang_cl /Zi /c -### -- %s 2>&1 | FileCheck -check-prefix=Zi %s
 // Zi: "-gcodeview"
-// Zi: "-debug-info-kind=limited"
+// Zi: "-debug-info-kind=constructor"
 
 // RUN: %clang_cl /Z7 /c -### -- %s 2>&1 | FileCheck -check-prefix=Z7 %s
 // Z7: "-gcodeview"
-// Z7: "-debug-info-kind=limited"
+// Z7: "-debug-info-kind=constructor"
 
 // RUN: %clang_cl /Zd /c -### -- %s 2>&1 | FileCheck -check-prefix=Z7GMLT %s
 // Z7GMLT: "-gcodeview"
@@ -557,7 +557,7 @@
 // which made it "win". This test could not detect that bug.
 // RUN: %clang_cl /Z7 -gdwarf /c -### -- %s 2>&1 | FileCheck -check-prefix=Z7_gdwarf %s
 // Z7_gdwarf: "-gcodeview"
-// Z7_gdwarf: "-debug-info-kind=limited"
+// Z7_gdwarf: "-debug-info-kind=constructor"
 // Z7_gdwarf: "-dwarf-version=4"
 
 // RUN: %clang_cl -fmsc-version=1800 -TP -### -- %s 2>&1 | FileCheck -check-prefix=CXX11 %s

clang/test/Driver/clang-g-opts.c

@@ -31,7 +31,7 @@
 // RUN:             | FileCheck --check-prefix=CHECK-WITH-G-DWARF2 %s
 
 // CHECK-WITHOUT-G-NOT: -debug-info-kind
-// CHECK-WITH-G: "-debug-info-kind=limited"
+// CHECK-WITH-G: "-debug-info-kind=constructor"
 // CHECK-WITH-G: "-dwarf-version=4"
 // CHECK-WITH-G-DWARF2: "-dwarf-version=2"
 

clang/test/Driver/cuda-dwarf-2.cu

@@ -49,7 +49,7 @@
 
 // HAS_DEBUG-NOT: warning: debug
 // HAS_DEBUG: "-fcuda-is-device"
-// HAS_DEBUG-SAME: "-debug-info-kind={{limited|line-tables-only}}"
+// HAS_DEBUG-SAME: "-debug-info-kind={{constructor|line-tables-only}}"
 // HAS_DEBUG-SAME: "-dwarf-version=2"
 // HAS_DEBUG: ptxas
 // HAS_DEBUG-SAME: "-g"

clang/test/Driver/debug-options-as.c

@@ -23,7 +23,7 @@
 // RUN:   | FileCheck %s
 //
 // CHECK: "-cc1as"
-// CHECK: "-debug-info-kind=limited"
+// CHECK: "-debug-info-kind=constructor"
 
 // Check to make sure clang with -g on a .s file gets passed -dwarf-debug-producer.
 // rdar://12955296

clang/test/Driver/debug-options.c

@@ -274,18 +274,18 @@
 // GLIO_ONLY_DWARF2: "-dwarf-version=2"
 //
 // G_ONLY: "-cc1"
-// G_ONLY: "-debug-info-kind=limited"
+// G_ONLY: "-debug-info-kind=constructor"
 //
 // These tests assert that "-gline-tables-only" "-g" uses the latter,
 // but otherwise not caring about the DebugInfoKind.
 // G_ONLY_DWARF2: "-cc1"
-// G_ONLY_DWARF2: "-debug-info-kind={{standalone|limited}}"
+// G_ONLY_DWARF2: "-debug-info-kind={{standalone|constructor}}"
 // G_ONLY_DWARF2: "-dwarf-version=2"
 //
 // G_STANDALONE: "-cc1"
 // G_STANDALONE: "-debug-info-kind=standalone"
 // G_LIMITED: "-cc1"
-// G_LIMITED: "-debug-info-kind=limited"
+// G_LIMITED: "-debug-info-kind=constructor"
 // G_DWARF2: "-dwarf-version=2"
 // G_DWARF4: "-dwarf-version=4"
 //
@@ -339,7 +339,7 @@
 // NOCI: "-gno-column-info"
 //
 // GEXTREFS: "-dwarf-ext-refs" "-fmodule-format=obj"
-// GEXTREFS: "-debug-info-kind={{standalone|limited}}"
+// GEXTREFS: "-debug-info-kind={{standalone|constructor}}"
 
 // RUN: not %clang -cc1 -debug-info-kind=watkind 2>&1 | FileCheck -check-prefix=BADSTRING1 %s
 // BADSTRING1: error: invalid value 'watkind' in '-debug-info-kind=watkind'

clang/test/Driver/integrated-as.s

@@ -27,19 +27,19 @@
 // XA_INCLUDE2: "-Ifoo_dir"
 
 // RUN: %clang -### -target x86_64--- -c -integrated-as %s -gdwarf-4 -gdwarf-2 2>&1 | FileCheck --check-prefix=DWARF2 %s
-// DWARF2: "-debug-info-kind=limited" "-dwarf-version=2"
+// DWARF2: "-debug-info-kind=constructor" "-dwarf-version=2"
 
 // RUN: %clang -### -target x86_64--- -c -integrated-as %s -gdwarf-3 2>&1 | FileCheck --check-prefix=DWARF3 %s
-// DWARF3: "-debug-info-kind=limited" "-dwarf-version=3"
+// DWARF3: "-debug-info-kind=constructor" "-dwarf-version=3"
 
 // RUN: %clang -### -target x86_64--- -c -integrated-as %s -gdwarf-4 2>&1 | FileCheck --check-prefix=DWARF4 %s
-// DWARF4: "-debug-info-kind=limited" "-dwarf-version=4"
+// DWARF4: "-debug-info-kind=constructor" "-dwarf-version=4"
 
 // RUN: %clang -### -target x86_64--- -c -integrated-as %s -Xassembler -gdwarf-2 2>&1 | FileCheck --check-prefix=DWARF2XASSEMBLER %s
-// DWARF2XASSEMBLER: "-debug-info-kind=limited" "-dwarf-version=2"
+// DWARF2XASSEMBLER: "-debug-info-kind=constructor" "-dwarf-version=2"
 
 // RUN: %clang -### -target x86_64--- -c -integrated-as %s -Wa,-gdwarf-2 2>&1 | FileCheck --check-prefix=DWARF2WA %s
-// DWARF2WA: "-debug-info-kind=limited" "-dwarf-version=2"
+// DWARF2WA: "-debug-info-kind=constructor" "-dwarf-version=2"
 
 // A dwarf version number that driver can't parse is just stuffed in.
 // RUN: %clang -### -target x86_64--- -c -integrated-as %s -Wa,-gdwarf-huh 2>&1 | FileCheck --check-prefix=BOGODWARF %s

clang/test/Driver/myriad-toolchain.c

@@ -83,7 +83,7 @@
 // NOSTDLIB-NOT: "-lc"
 
 // RUN: %clang -### -c -g %s -target sparc-myriad 2>&1 | FileCheck -check-prefix=G_SPARC %s
-// G_SPARC: "-debug-info-kind=limited" "-dwarf-version=2"
+// G_SPARC: "-debug-info-kind=constructor" "-dwarf-version=2"
 
 // RUN: %clang -### -c %s -target sparc-myriad-rtems -fuse-init-array 2>&1 \
 // RUN: | FileCheck -check-prefix=USE-INIT-ARRAY %s

clang/test/Driver/openmp-offload-gpu.c

@@ -241,7 +241,7 @@
 
 // HAS_DEBUG-NOT: warning: debug
 // HAS_DEBUG: "-triple" "nvptx64-nvidia-cuda"
-// HAS_DEBUG-SAME: "-debug-info-kind={{limited|line-tables-only}}"
+// HAS_DEBUG-SAME: "-debug-info-kind={{constructor|line-tables-only}}"
 // HAS_DEBUG-SAME: "-dwarf-version=2"
 // HAS_DEBUG-SAME: "-fopenmp-is-device"
 // HAS_DEBUG: ptxas

clang/test/Driver/split-debug.c

@@ -68,18 +68,18 @@
 // RUN: FileCheck -check-prefix=CHECK-NOINLINE-WITHOUT-SPLIT < %t %s
 //
 // CHECK-NOINLINE-WITHOUT-SPLIT: "-fno-split-dwarf-inlining"
-// CHECK-NOINLINE-WITHOUT-SPLIT: "-debug-info-kind=limited"
+// CHECK-NOINLINE-WITHOUT-SPLIT: "-debug-info-kind=constructor"
 
 // RUN: %clang -target x86_64-unknown-linux-gnu -gmlt -gsplit-dwarf -fno-split-dwarf-inlining -S -### %s 2> %t
 // RUN: FileCheck -check-prefix=CHECK-SPLIT-WITH-GMLT < %t %s
 //
-// CHECK-SPLIT-WITH-GMLT: "-debug-info-kind=limited"
+// CHECK-SPLIT-WITH-GMLT: "-debug-info-kind=constructor"
 // CHECK-SPLIT-WITH-GMLT: "-split-dwarf-output"
 
 // RUN: %clang -target x86_64-unknown-linux-gnu -gsplit-dwarf -fno-split-dwarf-inlining -S -### %s 2> %t
 // RUN: FileCheck -check-prefix=CHECK-SPLIT-WITH-NOINL < %t %s
 //
-// CHECK-SPLIT-WITH-NOINL: "-debug-info-kind=limited"
+// CHECK-SPLIT-WITH-NOINL: "-debug-info-kind=constructor"
 // CHECK-SPLIT-WITH-NOINL: "-split-dwarf-output"
 
 // RUN: %clang -target x86_64-unknown-linux-gnu -gsplit-dwarf -gmlt -fsplit-dwarf-inlining -S -### %s 2> %t
@@ -92,7 +92,7 @@
 // RUN: %clang -target x86_64-unknown-linux-gnu -gmlt -gsplit-dwarf -S -### %s 2> %t
 // RUN: FileCheck -check-prefix=CHECK-SPLIT-OVER-GMLT < %t %s
 //
-// CHECK-SPLIT-OVER-GMLT: "-debug-info-kind=limited"
+// CHECK-SPLIT-OVER-GMLT: "-debug-info-kind=constructor"
 // CHECK-SPLIT-OVER-GMLT: "-split-dwarf-file"
 // CHECK-SPLIT-OVER-GMLT: "-split-dwarf-output"
 
@@ -117,6 +117,6 @@
 // RUN: %clang -target x86_64-unknown-linux-gnu -g0 -gsplit-dwarf=split -S -### %s 2> %t
 // RUN: FileCheck -check-prefix=CHECK-SPLIT-OVER-G0 < %t %s
 //
-// CHECK-SPLIT-OVER-G0: "-debug-info-kind=limited"
+// CHECK-SPLIT-OVER-G0: "-debug-info-kind=constructor"
 // CHECK-SPLIT-OVER-G0: "-split-dwarf-file"
 // CHECK-SPLIT-OVER-G0: "-split-dwarf-output"

lldb/test/Shell/SymbolFile/PDB/Inputs/ClassLayoutTest.cpp

@@ -106,6 +106,7 @@ class Class : public Base { // Test base class.
 int main() {
   MemberTest::Base B1;
   B1.Get();
+  MemberTest::Class C1;
   MemberTest::Class::StaticMemberFunc(1, 10, 2);
   return 0;
 }