[llvm-objdump] --source: drop the warning when there is no debug info

Warnings have been added for three cases (PR41905): (1) missing debug info, (2)
the source file cannot be found, (3) the debug info points at a line beyond the
end of the file.

(1) is probably less useful. This was brought up once on
http://lists.llvm.org/pipermail/llvm-dev/2020-April/141264.html and two
internal users mentioned it to me that it was annoying. (I personally
find the warning confusing, too.)

Users specify --source to get additional information if sources happen to be
available.  If sources are not available, it should be obvious as the output
will have no interleaved source lines. The warning can be especially annoying
when using llvm-objdump -S on a bunch of files.

This patch drops the warning when there is no debug info.
(If LLVMSymbolizer::symbolizeCode returns an `Error`, there will still be
an error. There is currently no test for an `Error` return value.
The only code path is probably a broken symbol table, but we probably already emit a warning
in that case)

`source-interleave-prefix.test` has an inappropriate "malformed" test - the test simply has no
.debug_* because new llc does not produce debug info when the filename is empty (invalid).
I have tried tampering the header of .debug_info/.debug_line but llvm-symbolizer does not warn.
This patch does not intend to add the missing test coverage.

Differential Revision: https://reviews.llvm.org/D88715

test/tools/llvm-objdump/X86/source-interleave-no-debug-info.test

@@ -1,15 +1,13 @@
 ## Test that if an object has no debug information, only the disassembly is
-## printed when --source is specified, and that we emit a warning.
+## printed when --source is specified, and that we do not emit a warning.
 
 # RUN: sed -e "s,SRC_COMPDIR,%/p/Inputs,g" %p/Inputs/source-interleave.ll > %t.ll
 # RUN: llc -o %t.o -filetype=obj -mtriple=x86_64-pc-linux %t.ll
 # RUN: llvm-objcopy --strip-debug %t.o %t2.o
 
 # RUN: llvm-objdump --source %t.o | FileCheck %s --check-prefixes=CHECK,SOURCE
-# RUN: llvm-objdump --source %t2.o 2> %t2.e | FileCheck %s --check-prefixes=CHECK --implicit-check-not='main()'
-# RUN: FileCheck %s --input-file %t2.e --check-prefixes=WARN
+# RUN: llvm-objdump --source %t2.o 2>&1 | FileCheck %s --check-prefixes=CHECK --implicit-check-not='main()' --implicit-check-not=warning:
 
-# WARN:        warning: '{{.*}}2.o': failed to parse debug information
 # CHECK:       0000000000000010 <main>:
 # SOURCE-NEXT: ; int main() {
 # CHECK-NEXT:   10:   55                      pushq   %rbp

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

@@ -24,15 +24,6 @@
 ; 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
 
-;; Test malformed input.
-
-; RUN: sed -e "s,SRC_COMPDIR,,g" -e "s,filename: \"source-interleave-x86_64.c\",filename: \"\",g" \
-; RUN:   %p/Inputs/source-interleave.ll > %t-malformed.ll
-; RUN: llc -o %t-malformed.o -filetype=obj -mtriple=x86_64-pc-linux %t-malformed.ll
-; RUN: llvm-objdump --prefix myprefix --source %t-malformed.o 2>&1 | \
-; RUN:   FileCheck %s --check-prefix=CHECK-MALFORMED -DFILE=%t-malformed.o
-; CHECK-MALFORMED: warning: '[[FILE]]': failed to parse debug information for [[FILE]]
-
 ;; 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 | \

tools/llvm-objdump/llvm-objdump.cpp

@@ -947,8 +947,8 @@ protected:
   std::unordered_map<std::string, std::vector<StringRef>> LineCache;
   // Keep track of missing sources.
   StringSet<> MissingSources;
-  // Only emit 'no debug info' warning once.
-  bool WarnedNoDebugInfo;
+  // Only emit 'invalid debug info' warning once.
+  bool WarnedInvalidDebugInfo = false;
 
 private:
   bool cacheSource(const DILineInfo& LineInfoFile);
@@ -962,8 +962,7 @@ private:
 
 public:
   SourcePrinter() = default;
-  SourcePrinter(const ObjectFile *Obj, StringRef DefaultArch)
-      : Obj(Obj), WarnedNoDebugInfo(false) {
+  SourcePrinter(const ObjectFile *Obj, StringRef DefaultArch) : Obj(Obj) {
     symbolize::LLVMSymbolizer::Options SymbolizerOpts;
     SymbolizerOpts.PrintFunctions =
         DILineInfoSpecifier::FunctionNameKind::LinkageName;
@@ -1018,22 +1017,17 @@ void SourcePrinter::printSourceLine(formatted_raw_ostream &OS,
     return;
 
   DILineInfo LineInfo = DILineInfo();
-  auto ExpectedLineInfo = Symbolizer->symbolizeCode(*Obj, Address);
+  Expected<DILineInfo> ExpectedLineInfo =
+      Symbolizer->symbolizeCode(*Obj, Address);
   std::string ErrorMessage;
-  if (!ExpectedLineInfo)
-    ErrorMessage = toString(ExpectedLineInfo.takeError());
-  else
+  if (ExpectedLineInfo) {
     LineInfo = *ExpectedLineInfo;
-
-  if (LineInfo.FileName == DILineInfo::BadString) {
-    if (!WarnedNoDebugInfo) {
-      std::string Warning =
-          "failed to parse debug information for " + ObjectFilename.str();
-      if (!ErrorMessage.empty())
-        Warning += ": " + ErrorMessage;
-      reportWarning(Warning, ObjectFilename);
-      WarnedNoDebugInfo = true;
-    }
+  } else if (!WarnedInvalidDebugInfo) {
+    WarnedInvalidDebugInfo = true;
+    // TODO Untested.
+    reportWarning("failed to parse debug information: " +
+                      toString(ExpectedLineInfo.takeError()),
+                  ObjectFilename);
   }
 
   if (!Prefix.empty() && sys::path::is_absolute_gnu(LineInfo.FileName)) {