Avoid emitting redundant or unusable directories in DIFile metadata entries.

As discussed on llvm-dev recently, Clang currently emits redundant
directories in DIFile entries, such as

  .file	     1 "/Volumes/Data/llvm" "/Volumes/Data/llvm/tools/clang/test/CodeGen/debug-info-abspath.c"

This patch looks at any common prefix between the compilation
directory and the (absolute) file path and strips the redundant
part. More importantly it leaves the compilation directory empty if
the two paths have no common prefix.

After this patch the above entry is (assuming a compilation dir of "/Volumes/Data/llvm/_build"):

  .file 1 "/Volumes/Data/llvm" "tools/clang/test/CodeGen/debug-info-abspath.c"

When building the FileCheck binary with debug info, this patch makes
the build artifacts ~1kb smaller.

Differential Revision: https://reviews.llvm.org/D55085

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@348154 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/CGDebugInfo.cpp

@@ -181,8 +181,7 @@ void CGDebugInfo::setLocation(SourceLocation Loc) {
   SourceManager &SM = CGM.getContext().getSourceManager();
   auto *Scope = cast<llvm::DIScope>(LexicalBlockStack.back());
   PresumedLoc PCLoc = SM.getPresumedLoc(CurLoc);
-
-  if (PCLoc.isInvalid() || Scope->getFilename() == PCLoc.getFilename())
+  if (PCLoc.isInvalid() || Scope->getFile() == getOrCreateFile(CurLoc))
     return;
 
   if (auto *LBF = dyn_cast<llvm::DILexicalBlockFile>(Scope)) {
@@ -410,13 +409,13 @@ llvm::DIFile *CGDebugInfo::getOrCreateFile(SourceLocation Loc) {
   SourceManager &SM = CGM.getContext().getSourceManager();
   PresumedLoc PLoc = SM.getPresumedLoc(Loc);
 
-  if (PLoc.isInvalid() || StringRef(PLoc.getFilename()).empty())
+  StringRef FileName = PLoc.getFilename();
+  if (PLoc.isInvalid() || FileName.empty())
     // If the location is not valid then use main input file.
     return getOrCreateMainFile();
 
   // Cache the results.
-  const char *fname = PLoc.getFilename();
-  auto It = DIFileCache.find(fname);
+  auto It = DIFileCache.find(FileName.data());
 
   if (It != DIFileCache.end()) {
     // Verify that the information still exists.
@@ -431,11 +430,41 @@ llvm::DIFile *CGDebugInfo::getOrCreateFile(SourceLocation Loc) {
   if (CSKind)
     CSInfo.emplace(*CSKind, Checksum);
 
-  llvm::DIFile *F = DBuilder.createFile(
-      remapDIPath(PLoc.getFilename()), remapDIPath(getCurrentDirname()), CSInfo,
-      getSource(SM, SM.getFileID(Loc)));
+  StringRef Dir;
+  StringRef File;
+  std::string RemappedFile = remapDIPath(FileName);
+  std::string CurDir = remapDIPath(getCurrentDirname());
+  SmallString<128> DirBuf;
+  SmallString<128> FileBuf;
+  if (llvm::sys::path::is_absolute(RemappedFile)) {
+    // Strip the common prefix (if it is more than just "/") from current
+    // directory and FileName for a more space-efficient encoding.
+    auto FileIt = llvm::sys::path::begin(RemappedFile);
+    auto FileE = llvm::sys::path::end(RemappedFile);
+    auto CurDirIt = llvm::sys::path::begin(CurDir);
+    auto CurDirE = llvm::sys::path::end(CurDir);
+    for (; CurDirIt != CurDirE && *CurDirIt == *FileIt; ++CurDirIt, ++FileIt)
+      llvm::sys::path::append(DirBuf, *CurDirIt);
+    if (std::distance(llvm::sys::path::begin(CurDir), CurDirIt) == 1) {
+      // The common prefix only the root; stripping it would cause
+      // LLVM diagnostic locations to be more confusing.
+      Dir = {};
+      File = RemappedFile;
+    } else {
+      for (; FileIt != FileE; ++FileIt)
+        llvm::sys::path::append(FileBuf, *FileIt);
+      Dir = DirBuf;
+      File = FileBuf;
+    }
+  } else {
+    Dir = CurDir;
+    File = RemappedFile;
+  }
+  llvm::DIFile *F =
+      DBuilder.createFile(File, Dir, CSInfo,
+                          getSource(SM, SM.getFileID(Loc)));
 
-  DIFileCache[fname].reset(F);
+  DIFileCache[FileName.data()].reset(F);
   return F;
 }
 

lib/CodeGen/CodeGenAction.cpp

@@ -549,12 +549,16 @@ const FullSourceLoc BackendConsumer::getBestLocationFromDebugLoc(
   SourceLocation DILoc;
 
   if (D.isLocationAvailable()) {
-    D.getLocation(&Filename, &Line, &Column);
-    const FileEntry *FE = FileMgr.getFile(Filename);
-    if (FE && Line > 0) {
-      // If -gcolumn-info was not used, Column will be 0. This upsets the
-      // source manager, so pass 1 if Column is not set.
-      DILoc = SourceMgr.translateFileLineCol(FE, Line, Column ? Column : 1);
+    D.getLocation(Filename, Line, Column);
+    if (Line > 0) {
+      const FileEntry *FE = FileMgr.getFile(Filename);
+      if (!FE)
+        FE = FileMgr.getFile(D.getAbsolutePath());
+      if (FE) {
+        // If -gcolumn-info was not used, Column will be 0. This upsets the
+        // source manager, so pass 1 if Column is not set.
+        DILoc = SourceMgr.translateFileLineCol(FE, Line, Column ? Column : 1);
+      }
     }
     BadDebugInfo = DILoc.isInvalid();
   }

test/CodeGen/debug-info-abspath.c

@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -debug-info-kind=limited -triple %itanium_abi_triple \
+// RUN:   %s -emit-llvm -o - | FileCheck %s
+
+// RUN: cp %s %t.c
+// RUN: %clang_cc1 -debug-info-kind=limited -triple %itanium_abi_triple \
+// RUN:   %t.c -emit-llvm -o - | FileCheck %s --check-prefix=INTREE
+void foo() {}
+
+// Since %s is an absolute path, directory should be a nonempty
+// prefix, but the CodeGen part should be part of the filename.
+
+// CHECK: DIFile(filename: "{{.*}}CodeGen{{.*}}debug-info-abspath.c"
+// CHECK-SAME:   directory: "{{.+}}")
+
+// INTREE: DIFile({{.*}}directory: "{{.+}}CodeGen{{.*}}")

test/CodeGen/debug-prefix-map.c

@@ -17,18 +17,22 @@ void test_rewrite_includes() {
 }
 
 // CHECK-NO-MAIN-FILE-NAME: !DIFile(filename: "/var/empty{{/|\\5C}}<stdin>"
-// CHECK-NO-MAIN-FILE-NAME: !DIFile(filename: "/var/empty{{[/\\]}}{{.*}}"
-// CHECK-NO-MAIN-FILE-NAME: !DIFile(filename: "/var/empty{{[/\\]}}Inputs/stdio.h"
+// CHECK-NO-MAIN-FILE-NAME: !DIFile(filename: "/var/empty{{[/\\]}}{{.*}}",
+// CHECK-NO-MAIN-FILE-NAME-SAME:    directory: "")
+// CHECK-NO-MAIN-FILE-NAME: !DIFile(filename: "/var/empty{{[/\\]}}Inputs/stdio.h",
+// CHECK-NO-MAIN-FILE-NAME-SAME:    directory: "")
 // CHECK-NO-MAIN-FILE-NAME-NOT: !DIFile(filename:
 
 // CHECK-EVIL: !DIFile(filename: "/var=empty{{[/\\]}}{{.*}}"
-// CHECK-EVIL: !DIFile(filename: "/var=empty{{[/\\]}}Inputs/stdio.h"
+// CHECK-EVIL: !DIFile(filename: "/var=empty{{[/\\]}}{{.*}}Inputs/stdio.h",
+// CHECK-EVIL-SAME:    directory: "")
 // CHECK-EVIL-NOT: !DIFile(filename:
 
 // CHECK: !DIFile(filename: "/var/empty{{[/\\]}}{{.*}}"
-// CHECK: !DIFile(filename: "/var/empty{{[/\\]}}Inputs/stdio.h"
+// CHECK: !DIFile(filename: "/var/empty{{[/\\]}}{{.*}}Inputs/stdio.h",
+// CHECK-SAME:    directory: "")
 // CHECK-NOT: !DIFile(filename:
 
-// CHECK-COMPILATION-DIR: !DIFile(filename: "/var/empty{{[/\\]}}{{.*}}", directory: "/var/empty")
-// CHECK-COMPILATION-DIR: !DIFile(filename: "/var/empty{{[/\\]}}Inputs/stdio.h", directory: "/var/empty")
+// CHECK-COMPILATION-DIR: !DIFile(filename: "{{.*}}", directory: "/var/empty")
+// CHECK-COMPILATION-DIR: !DIFile(filename: "Inputs/stdio.h", directory: "/var/empty")
 // CHECK-COMPILATION-DIR-NOT: !DIFile(filename:

test/Modules/module-debuginfo-prefix.m

@@ -20,4 +20,4 @@
 @import DebugObjC;
 #endif
 
-// CHECK: !DIFile({{.*}}"/OVERRIDE/DebugObjC.h"
+// CHECK: !DIFile(filename: "/OVERRIDE/DebugObjC.h", directory: "")