Print discriminators when printing .debug_line in GNU style.

Summary:
gnu addr2line prints DWARF line table discriminators like so:

<file>:<line> (discriminator <Number>)

This matches that behavior.

Document how and when --output-style=GNU prints discriminators

Add test for new GNU-style discriminator printing.

Reviewers: rupprecht, labath, jhenderson

Subscribers: aprantl, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73318
diff --git a/llvm/docs/CommandGuide/llvm-symbolizer.rst b/llvm/docs/CommandGuide/llvm-symbolizer.rst
index bb60246..10f72a0 100644
--- a/llvm/docs/CommandGuide/llvm-symbolizer.rst
+++ b/llvm/docs/CommandGuide/llvm-symbolizer.rst
@@ -227,6 +227,9 @@
     topmost caller when inlined frames are not shown and :option:`--use-symbol-table`
     is on.
 
+  * Prints an address's debug-data discriminator when it is non-zero. One way to
+    produce discriminators is to compile with clang's -fdebug-info-for-profiling.
+
   .. code-block:: console
 
     $ llvm-symbolizer --obj=inlined.elf 0x4004be 0x400486 -p
@@ -244,6 +247,10 @@
     baz() at /tmp/test.cpp:11
     foo() at /tmp/test.cpp:6
 
+    $ clang -g -fdebug-info-for-profiling test.cpp -o profiling.elf
+    $ llvm-symbolizer --output-style=GNU --obj=profiling.elf 0x401167 -p -i=0
+    main at /tmp/test.cpp:15 (discriminator 2)
+
 .. option:: --pretty-print, -p
 
   Print human readable output. If :option:`--inlining` is specified, the
diff --git a/llvm/lib/DebugInfo/Symbolize/DIPrinter.cpp b/llvm/lib/DebugInfo/Symbolize/DIPrinter.cpp
index c5b71ba..223b663 100644
--- a/llvm/lib/DebugInfo/Symbolize/DIPrinter.cpp
+++ b/llvm/lib/DebugInfo/Symbolize/DIPrinter.cpp
@@ -79,6 +79,8 @@
     OS << Filename << ":" << Info.Line;
     if (Style == OutputStyle::LLVM)
       OS << ":" << Info.Column;
+    else if (Style == OutputStyle::GNU && Info.Discriminator != 0)
+      OS << " (discriminator " << Info.Discriminator << ")";
     OS << "\n";
     printContext(Filename, Info.Line);
     return;
diff --git a/llvm/test/tools/llvm-symbolizer/discriminator.test b/llvm/test/tools/llvm-symbolizer/discriminator.test
new file mode 100644
index 0000000..1cc3987
--- /dev/null
+++ b/llvm/test/tools/llvm-symbolizer/discriminator.test
@@ -0,0 +1,20 @@
+# Check that llvm-symbolizer prints line-table discriminators properly.
+
+RUN: llvm-symbolizer --output-style=GNU -f --obj=%p/Inputs/discrim 0x400590 0x400575 \
+RUN:   | FileCheck %s --check-prefix=GNU --match-full-lines
+RUN: llvm-symbolizer --output-style=LLVM -f --obj=%p/Inputs/discrim 0x400590 0x400575 \
+RUN:   | FileCheck %s --check-prefix=LLVM --match-full-lines
+
+GNU: foo
+GNU: /tmp{{[\\/]}}discrim.c:5
+GNU: main
+GNU: /tmp{{[\\/]}}discrim.c:10
+GNU: foo
+GNU: /tmp{{[\\/]}}discrim.c:5 (discriminator 2)
+
+LLVM: foo
+LLVM: /tmp{{[\\/]}}discrim.c:5:7
+LLVM: main
+LLVM: /tmp{{[\\/]}}discrim.c:10:0
+LLVM: foo
+LLVM: /tmp{{[\\/]}}discrim.c:5:17