[DebugInfo] Assign best possible debugloc to bundle (llvm#164573)

The debug info attached to the BUNDLE is the first instruction in the
BUNDLE, even if a better debug info (line:column) is present in the
later instructions of the bundle. The patch tries to get a better debug
info first. If not, then a worse debug info without line number is
chosen.

---------

Co-authored-by: Vladislav Dzhidzhoev <[email protected]>
Co-authored-by: Orlando Cazalet-Hyams <[email protected]>

Author: 3 people

llvm/lib/CodeGen/MachineInstrBundle.cpp

@@ -83,15 +83,21 @@ llvm::createUnpackMachineBundles(
   return new UnpackMachineBundles(std::move(Ftor));
 }
 
-/// Return the first found DebugLoc that has a DILocation, given a range of
-/// instructions. The search range is from FirstMI to LastMI (exclusive). If no
-/// DILocation is found, then an empty location is returned.
+/// Return the first DebugLoc that has line number information, given a
+/// range of instructions. The search range is from FirstMI to LastMI
+/// (exclusive). Otherwise return the first DILocation or an empty location if
+/// there are none.
 static DebugLoc getDebugLoc(MachineBasicBlock::instr_iterator FirstMI,
                             MachineBasicBlock::instr_iterator LastMI) {
-  for (auto MII = FirstMI; MII != LastMI; ++MII)
-    if (MII->getDebugLoc())
-      return MII->getDebugLoc();
-  return DebugLoc();
+  DebugLoc DL;
+  for (auto MII = FirstMI; MII != LastMI; ++MII) {
+    if (DebugLoc MIIDL = MII->getDebugLoc()) {
+      if (MIIDL.getLine() != 0)
+        return MIIDL;
+      DL = MIIDL.get();
+    }
+  }
+  return DL;
 }
 
 /// Check if target reg is contained in given lists, which are:

llvm/test/DebugInfo/Hexagon/lit.local.cfg

@@ -0,0 +1,2 @@
+if not "Hexagon" in config.root.targets:
+    config.unsupported = True

llvm/test/DebugInfo/Hexagon/packet-debug.mir

@@ -0,0 +1,48 @@
+# RUN: llc -mtriple=hexagon -run-pass hexagon-packetizer %s -o - | FileCheck %s
+
+# CHECK-LABEL: name: factorial
+
+# The first bundle in bb.0 should have debug-location !19 (line 9),
+# not !18 (line 0) from the DBG_VALUE instructions.
+# CHECK: bb.0:
+# CHECK: BUNDLE {{.*}}line: 9
+
+--- |
+  define void @factorial() { ret void }
+
+  !llvm.dbg.cu = !{!2}
+  !llvm.module.flags = !{!6, !7}
+
+  !2 = distinct !DICompileUnit(language: DW_LANG_C11, file: !3, producer: "test", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+  !3 = !DIFile(filename: "fact.c", directory: "/test")
+  !5 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !6 = !{i32 2, !"Debug Info Version", i32 3}
+  !7 = !{i32 1, !"wchar_size", i32 4}
+  !12 = distinct !DISubprogram(name: "factorial", scope: !3, file: !3, line: 6, type: !13, scopeLine: 7, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2)
+  !13 = !DISubroutineType(types: !14)
+  !14 = !{!5, !5}
+  !16 = !DILocalVariable(name: "i", arg: 1, scope: !12, file: !3, line: 6, type: !5)
+  !18 = !DILocation(line: 0, scope: !12)
+  !19 = !DILocation(line: 9, column: 9, scope: !12)
+  !21 = !DILocation(line: 9, column: 7, scope: !12)
+
+...
+---
+name:            factorial
+alignment:       16
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $r0
+
+    DBG_VALUE $r0, $noreg, !16, !DIExpression(), debug-location !18
+    $r2 = A2_tfr $r0
+    DBG_VALUE $r2, $noreg, !16, !DIExpression(), debug-location !18
+    renamable $p0 = C2_cmpeqi killed $r0, 1, debug-location !19
+    renamable $r0 = A2_tfrsi 1
+    J2_jumpt killed $p0, %bb.1, implicit-def $pc, debug-location !21
+
+  bb.1:
+    PS_jmpret $r31, implicit-def dead $pc
+
+...