From 51fc742ce716a09359f4f87ffe3876cb7ff9479d Mon Sep 17 00:00:00 2001
From: Fangrui Song <i@maskray.me>
Date: Mon, 12 Jul 2021 15:46:20 -0700
Subject: [PATCH] [Driver] Let -fno-integrated-as -gdwarf-5 use
 -fdwarf-directory-asm

While GNU as only allows the directory form of the .file directive for DWARF v5,
the integrated assembler prefers the directory form on all DWARF versions
(-fdwarf-directory-asm).

We currently set CC1 -fno-dwarf-directory-asm for -fno-integrated-as -gdwarf-5
which may cause the directory entry 0 and the filename entry 0 to be incorrect
(see D105662 and the example below). This patch makes -fno-integrated-as -gdwarf-5 use
-fdwarf-directory-asm as well.

```
cd /tmp/c

before
% clang -g -gdwarf-5 -fno-integrated-as e/a.c -S -o - | grep '\.file.*0'
        .file   0 "/tmp/c/e/a.c" md5 0x97e31cee64b4e58a4af8787512d735b6
% clang -g -gdwarf-5 -fno-integrated-as e/a.c -c
% llvm-dwarfdump a.o | grep include_directories
include_directories[  0] = "/tmp/c/e"

after
% clang -g -gdwarf-5 -fno-integrated-as e/a.c -S -o - | grep '\.file.*0'
        .file   0 "/tmp/c" "e/a.c" md5 0x97e31cee64b4e58a4af8787512d735b6
% clang -g -gdwarf-5 -fno-integrated-as e/a.c -c
% llvm-dwarfdump a.o | grep include_directories
include_directories[  0] = "/tmp/c"
```

Reviewed By: #debug-info, dblaikie, osandov

Differential Revision: https://reviews.llvm.org/D105835
---
 clang/lib/Driver/ToolChains/Clang.cpp | 19 ++++++++-----------
 clang/test/Driver/debug-options.c     | 11 +++++++++++
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 85204ceaa49a..4336a25f091c 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -490,14 +490,6 @@ static bool ShouldEnableAutolink(const ArgList &Args, const ToolChain &TC,
                       Default);
 }
 
-static bool ShouldDisableDwarfDirectory(const ArgList &Args,
-                                        const ToolChain &TC) {
-  bool UseDwarfDirectory =
-      Args.hasFlag(options::OPT_fdwarf_directory_asm,
-                   options::OPT_fno_dwarf_directory_asm, TC.useIntegratedAs());
-  return !UseDwarfDirectory;
-}
-
 // Convert an arg of the form "-gN" or "-ggdbN" or one of their aliases
 // to the corresponding DebugInfoKind.
 static codegenoptions::DebugInfoKind DebugLevelToInfoKind(const Arg &A) {
@@ -4175,6 +4167,14 @@ static void renderDebugOptions(const ToolChain &TC, const Driver &D,
     }
   }
 
+  // To avoid join/split of directory+filename, the integrated assembler prefers
+  // the directory form of .file on all DWARF versions. GNU as doesn't allow the
+  // form before DWARF v5.
+  if (!Args.hasFlag(options::OPT_fdwarf_directory_asm,
+                    options::OPT_fno_dwarf_directory_asm,
+                    TC.useIntegratedAs() || EffectiveDWARFVersion >= 5))
+    CmdArgs.push_back("-fno-dwarf-directory-asm");
+
   // Decide how to render forward declarations of template instantiations.
   // SCE wants full descriptions, others just get them in the name.
   if (DebuggerTuning == llvm::DebuggerKind::SCE)
@@ -5506,9 +5506,6 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
       CmdArgs.push_back("-fno-gnu-keywords");
   }
 
-  if (ShouldDisableDwarfDirectory(Args, TC))
-    CmdArgs.push_back("-fno-dwarf-directory-asm");
-
   if (!ShouldEnableAutolink(Args, TC, JA))
     CmdArgs.push_back("-fno-autolink");
 
diff --git a/clang/test/Driver/debug-options.c b/clang/test/Driver/debug-options.c
index 54a8a6a3f74a..3b1f1d555bbc 100644
--- a/clang/test/Driver/debug-options.c
+++ b/clang/test/Driver/debug-options.c
@@ -424,3 +424,14 @@
 // GDWARF64_VER:  error: invalid argument '-gdwarf64' only allowed with 'DWARFv3 or greater'
 // GDWARF64_32ARCH: error: invalid argument '-gdwarf64' only allowed with '64 bit architecture'
 // GDWARF64_ELF: error: invalid argument '-gdwarf64' only allowed with 'ELF platforms'
+
+/// Default to -fno-dwarf-directory-asm for -fno-integrated-as before DWARF v5.
+// RUN: %clang -### -target x86_64 -c -gdwarf-2 %s 2>&1 | FileCheck --check-prefix=DIRECTORY %s
+// RUN: %clang -### -target x86_64 -c -gdwarf-5 %s 2>&1 | FileCheck --check-prefix=DIRECTORY %s
+// RUN: %clang -### -target x86_64 -c -gdwarf-4 -fno-integrated-as %s 2>&1 | FileCheck --check-prefix=NODIRECTORY %s
+// RUN: %clang -### -target x86_64 -c -gdwarf-5 -fno-integrated-as %s 2>&1 | FileCheck --check-prefix=DIRECTORY %s
+
+// RUN: %clang -### -target x86_64 -c -gdwarf-4 -fno-dwarf-directory-asm %s 2>&1 | FileCheck --check-prefix=NODIRECTORY %s
+
+// DIRECTORY-NOT: "-fno-dwarf-directory-asm"
+// NODIRECTORY: "-fno-dwarf-directory-asm"