[llvm-objdump] Implement --prefix-strip option

The option `--prefix-strip` is only used when `--prefix` is not empty.
It removes N initial directories from absolute paths before adding the
prefix.

This matches GNU's objdump behavior.

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D96679

docs/CommandGuide/llvm-objdump.rst

@@ -172,6 +172,12 @@ OPTIONS
   When disassembling with the :option:`--source` option, prepend ``prefix`` to
   absolute paths.
 
+.. option:: --prefix-strip=<level>
+
+  When disassembling with the :option:`--source` option, strip out ``level``
+  initial directories from absolute paths. This option has no effect without
+  :option:`--prefix`.
+
 .. option:: --print-imm-hex
 
   Use hex format when printing immediate values in disassembly output.

docs/llvm-objdump.1

@@ -109,6 +109,11 @@ When disassembling instructions, do not print the instruction bytes.
 When disassembling, add
 .Ar PREFIX
 to absolute paths.
+.It Fl -prefix-strip Ns = Ns Ar LEVEL
+When disassembling, strip out
+.Ar LEVEL
+initial directories from absolute paths. This option has no effect without
+.Fl -prefix Ns = Ns PREFIX .
 .It Fl -print-imm-hex
 Use hex format for immediate values.
 .It Fl -private-header

test/tools/llvm-objdump/X86/source-interleave-prefix.test

@@ -12,8 +12,8 @@
 ; RUN: sed -e "s,SRC_COMPDIR,./Inputs,g" %p/Inputs/source-interleave.ll > %t-relative-path.ll
 ; RUN: llc -o %t-relative-path.o -filetype=obj -mtriple=x86_64-pc-linux %t-relative-path.ll
 ; RUN: llvm-objdump --prefix myprefix --source %t-relative-path.o 2>&1 | \
-; RUN:   FileCheck %s --check-prefix=CHECK-BROKEN-PREFIX -DFILE=%t-relative-path.o -DPREFIX=.
-; CHECK-BROKEN-PREFIX: warning: '[[FILE]]': failed to find source [[PREFIX]]/Inputs{{[/\\]}}source-interleave-x86_64.c
+; RUN:   FileCheck %s --check-prefix=CHECK-BROKEN-PREFIX -DFILE=%t-relative-path.o -DPREFIX=. -DCOMPDIR=/Inputs
+; CHECK-BROKEN-PREFIX: warning: '[[FILE]]': failed to find source [[PREFIX]][[COMPDIR]]{{[/\\]}}source-interleave-x86_64.c
 
 ;; Test invalid source interleave fixed by adding the correct prefix.
 
@@ -28,16 +28,64 @@
 ; RUN: sed -e "s,SRC_COMPDIR,%/p/Inputs,g" %p/Inputs/source-interleave.ll > %t-correct-prefix.ll
 ; RUN: llc -o %t-correct-prefix.o -filetype=obj -mtriple=x86_64-pc-linux %t-correct-prefix.ll
 ; RUN: llvm-objdump --prefix myprefix --source %t-correct-prefix.o 2>&1 | \
-; RUN:   FileCheck %s --check-prefix=CHECK-BROKEN-PREFIX -DFILE=%t-correct-prefix.o -DPREFIX=myprefix%/p
+; RUN:   FileCheck %s --check-prefix=CHECK-BROKEN-PREFIX -DFILE=%t-correct-prefix.o -DPREFIX=myprefix%/p -DCOMPDIR=/Inputs
 
 ;; Using only a prefix separator is the same as not using the `--prefix` option.
 
 ; RUN: llvm-objdump --prefix / --source %t-missing-prefix.o 2>&1 | \
-; RUN:   FileCheck %s --check-prefix=CHECK-BROKEN-PREFIX -DFILE=%t-missing-prefix.o -DPREFIX=''
+; RUN:   FileCheck %s --check-prefix=CHECK-BROKEN-PREFIX -DFILE=%t-missing-prefix.o -DPREFIX='' -DCOMPDIR=/Inputs
 
 ;; All trailing separators on the prefix are discarded.
 ;; The prefix 'myprefix//' is converted to 'myprefix'.
 
 ; RUN: llvm-objdump --prefix myprefix// --source %t-missing-prefix.o 2>&1 | \
-; RUN:   FileCheck %s --check-prefix=CHECK-BROKEN-PREFIX -DFILE=%t-missing-prefix.o -DPREFIX=myprefix
+; RUN:   FileCheck %s --check-prefix=CHECK-BROKEN-PREFIX -DFILE=%t-missing-prefix.o -DPREFIX=myprefix -DCOMPDIR=/Inputs
 
+;; Test invalid source interleave fixed by adding the correct prefix and
+;; stripping out an extra directory from the path.
+
+; RUN: sed -e "s,SRC_COMPDIR,/extra/Inputs,g" %p/Inputs/source-interleave.ll > %t-extra-path-prefix.ll
+; RUN: llc -o %t-extra-path-prefix.o -filetype=obj -mtriple=x86_64-pc-linux %t-extra-path-prefix.ll
+; RUN: llvm-objdump --prefix %p --prefix-strip 1 --source %t-extra-path-prefix.o 2>&1 | \
+; RUN:   FileCheck %s --check-prefix=CHECK-MISSING-PREFIX-FIX
+
+;; Test do not skip extra separators. The --prefix-strip should take into
+;; account each separator individually. Hence, to fix '/extra/Inputs'
+;; --prefix-strip needs to be 1. To fix '//extra/Inputs' --prefix-strip
+;; needs to be 2.
+
+; RUN: sed -e "s,SRC_COMPDIR,//extra/Inputs,g" %p/Inputs/source-interleave.ll > %t-extra-sep-path-prefix.ll
+; RUN: llc -o %t-extra-sep-path-prefix.o -filetype=obj -mtriple=x86_64-pc-linux %t-extra-sep-path-prefix.ll
+; RUN: llvm-objdump --prefix %p --prefix-strip 2 --source %t-extra-sep-path-prefix.o 2>&1 | \
+; RUN:   FileCheck %s --check-prefix=CHECK-MISSING-PREFIX-FIX
+
+;; Test --prefix-strip value of 0. No effect.
+;; SRC_COMPDIR is set to '/Inputs' before and after --prefix-strip 0.
+
+; RUN: llvm-objdump --prefix %p --prefix-strip 0 --source %t-missing-prefix.o 2>&1 | \
+; RUN:   FileCheck %s --check-prefix=CHECK-MISSING-PREFIX-FIX
+
+;; Test --prefix-strip value equal to the number of directory components.
+;; SRC_COMPDIR is set to '/Inputs' before --prefix-strip 1.
+;; SRC_COMPDIR becomes '' after --prefix-strip 1.
+
+; RUN: llvm-objdump --prefix %p/Inputs --prefix-strip 1 --source %t-missing-prefix.o 2>&1 | \
+; RUN:   FileCheck %s --check-prefix=CHECK-MISSING-PREFIX-FIX
+
+;; Test --prefix-strip value greater than the number of components.
+;; SRC_COMPDIR is set to '/Inputs' before --prefix-strip 2.
+;; SRC_COMPDIR becomes '' after --prefix-strip 2.
+
+; RUN: llvm-objdump --prefix %p/Inputs --prefix-strip 2 --source %t-missing-prefix.o 2>&1 | \
+; RUN:   FileCheck %s --check-prefix=CHECK-MISSING-PREFIX-FIX
+
+;; Test negative value --prefix-strip. Reports an error.
+
+; RUN: not llvm-objdump --prefix %p --prefix-strip '-1' --source %t-missing-prefix.o 2>&1 | \
+; RUN:   FileCheck %s --check-prefix=CHECK-INVALID-PREFIX-STRIP -DOPTION='-1'
+; CHECK-INVALID-PREFIX-STRIP: llvm-objdump{{.*}}: for the --prefix-strip option: '[[OPTION]]' value invalid for uint argument!
+
+;; Test text value --prefix-strip. Reports an error.
+
+; RUN: not llvm-objdump --prefix %p --prefix-strip foo --source %t-missing-prefix.o 2>&1 | \
+; RUN:   FileCheck %s --check-prefix=CHECK-INVALID-PREFIX-STRIP -DOPTION='foo'

tools/llvm-objdump/llvm-objdump.cpp

@@ -358,6 +358,12 @@ cl::opt<std::string> objdump::Prefix("prefix",
                                      cl::desc("Add prefix to absolute paths"),
                                      cl::cat(ObjdumpCat));
 
+cl::opt<uint32_t>
+    objdump::PrefixStrip("prefix-strip",
+                         cl::desc("Strip out initial directories from absolute "
+                                  "paths. No effect without --prefix"),
+                         cl::init(0), cl::cat(ObjdumpCat));
+
 enum DebugVarsFormat {
   DVDisabled,
   DVUnicode,
@@ -1031,6 +1037,27 @@ void SourcePrinter::printSourceLine(formatted_raw_ostream &OS,
   }
 
   if (!Prefix.empty() && sys::path::is_absolute_gnu(LineInfo.FileName)) {
+    // FileName has at least one character since is_absolute_gnu is false for
+    // an empty string.
+    assert(!LineInfo.FileName.empty());
+    if (PrefixStrip > 0) {
+      uint32_t Level = 0;
+      auto StrippedNameStart = LineInfo.FileName.begin();
+
+      // Path.h iterator skips extra separators. Therefore it cannot be used
+      // here to keep compatibility with GNU Objdump.
+      for (auto Pos = StrippedNameStart + 1, End = LineInfo.FileName.end();
+           Pos != End && Level < PrefixStrip; ++Pos) {
+        if (sys::path::is_separator(*Pos)) {
+          StrippedNameStart = Pos;
+          ++Level;
+        }
+      }
+
+      LineInfo.FileName =
+          std::string(StrippedNameStart, LineInfo.FileName.end());
+    }
+
     SmallString<128> FilePath;
     sys::path::append(FilePath, Prefix, LineInfo.FileName);
 

tools/llvm-objdump/llvm-objdump.h

@@ -42,6 +42,7 @@ extern cl::opt<std::string> MCPU;
 extern cl::opt<bool> NoShowRawInsn;
 extern cl::opt<bool> NoLeadingAddr;
 extern cl::opt<std::string> Prefix;
+extern cl::opt<uint32_t> PrefixStrip;
 extern cl::opt<bool> PrintImmHex;
 extern cl::opt<bool> PrivateHeaders;
 extern cl::opt<bool> Relocations;