[WebAssembly] Handle DebugLoc in DebugValueManager

[aheejin]

Summary

According to
https://llvm.org/docs/HowToUpdateDebugInfo.html#when-to-preserve-an-instruction-location,
when moving (and in our case cloning) within the same BB, the debug
location is preserved. But when moving / cloning to a different BB, we
preserve the debug location only if the destination BB contains the same
location. Currently we preserve the debug loc unconditionally in all
cases. This CL correctly handles the debug locs in DebugValueManager.

[dschuff]

llvm/lib/Target/WebAssembly/WebAssemblyDebugValueManager.cpp

229

[aheejin]

Typo fix

llvm/lib/Target/WebAssembly/WebAssemblyDebugValueManager.cpp

for (MachineBasicBlock::iterator MI = std::next(Def->getIterator()),
        MI != ME; ++MI) {
     if (std::find(DbgValues.begin(), DbgValues.end(), MI) == DbgValues.end()) {
       return false;
     }
   }
   return true;
 }
 
+// Returns true if any instruction in MBB has the same debug location as DL.
+// Also returns true if DL is an empty location.
+static bool hasSameDebugLoc(const MachineBasicBlock *MBB, DebugLoc DL) {
+  for (const auto &MI : *MBB)
+    if (MI.getDebugLoc() == DL)
+      return true;
+  return false;
+}
+
 // Sink 'Def', and also sink its eligible DBG_VALUEs to the place before
 // 'Insert'. Convert the original DBG_VALUEs into undefs.
 //
 // For DBG_VALUEs to sink properly, if 'Def' and 'Insert' are within the same
 // BB, 'Insert' should be below 'Def'; if they are in different BBs, 'Insert'
 // should be in one of 'Def's BBs successors. Def will be sunk regardless of the
 // location.
 //
void WebAssemblyDebugValueManager::sink(MachineInstr *Insert) {
   MachineFunction *MF = MBB->getParent();
 
   // Get the list of sinkable DBG_VALUEs. This should be done before sinking
   // Def, because we need to examine instructions between Def and Insert.
   SmallVector<MachineInstr *, 1> SinkableDbgValues =
       getSinkableDebugValues(Insert);
 
   // Sink Def first.
+  //
+  // When moving to a different BB, we preserve the debug loc only if the
+  // destination BB contains the same location. See
+  // https://llvm.org/docs/HowToUpdateDebugInfo.html#when-to-preserve-an-instruction-location.
+  if (Def->getParent() != MBB && !hasSameDebugLoc(MBB, Def->getDebugLoc()))
+      Def->setDebugLoc(DebugLoc());
   MBB->splice(Insert, Def->getParent(), Def);
 
   if (DbgValues.empty())
     return;
 
   // Clone sinkable DBG_VALUEs and insert them.
   SmallVector<MachineInstr *, 1> NewDbgValues;
   for (MachineInstr *DV : SinkableDbgValues) {
void WebAssemblyDebugValueManager::cloneSink(MachineInstr *Insert,
   MachineFunction *MF = MBB->getParent();
 
   SmallVector<MachineInstr *> SinkableDbgValues =
       getSinkableDebugValues(Insert);
 
   // Clone Def first.
   if (CloneDef) {
     MachineInstr *Clone = MF->CloneMachineInstr(Def);
+    // When cloning to a different BB, we preserve the debug loc only if the
+    // destination BB contains the same location. See
+    // https://llvm.org/docs/HowToUpdateDebugInfo.html#when-to-preserve-an-instruction-location.
+    if (Def->getParent() != MBB && !hasSameDebugLoc(MBB, Def->getDebugLoc()))
+      Clone->setDebugLoc(DebugLoc());
     if (NewReg != CurrentReg && NewReg.isValid())
       Clone->getOperand(0).setReg(NewReg);
     MBB->insert(Insert, Clone);
   }
 
   if (DbgValues.empty())
     return;
 

llvm/test/DebugInfo/WebAssembly/dbg-loc-reg-stackify.mir

+# RUN: llc -run-pass wasm-reg-stackify %s -o - | FileCheck %s
+
+--- |
+  target triple = "wasm32-unknown-unknown"
+
+  declare void @use(i32)
+
+  define void @sink_same_bb() {
+    unreachable
+  }
+  define void @clone_same_bb() {
+    unreachable
+  }
+  define void @clone_different_bb_0() {
+    unreachable
+  }
+  define void @clone_different_bb_1() {
+    unreachable
+  }
+
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!2, !3, !4}
+
+  !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, emissionKind: FullDebug)
+  !1 = !DIFile(filename: "test.c", directory: "")
+  !2 = !{i32 7, !"Dwarf Version", i32 5}
+  !3 = !{i32 2, !"Debug Info Version", i32 3}
+  !4 = !{i32 1, !"wchar_size", i32 4}
+  !6 = distinct !DISubprogram(name: "sink_same_bb", scope: !1, file: !1, line: 1, type: !7, scopeLine: 1, unit: !0)
+  !7 = !DISubroutineType(types: !8)
+  !8 = !{null}
+...
+
+---
+# Sinking within the same BB preserves the debug location.
+# CHECK-LABEL: name: sink_same_bb
+name: sink_same_bb
+liveins:
+  - { reg: '$arguments' }
+tracksRegLiveness: true
+body: |
+  bb.0:
+    liveins: $arguments
+    %0:i32 = CONST_I32 1, implicit-def $arguments, debug-location !DILocation(line:10, scope:!6)
+    NOP implicit-def $arguments
+    CALL @use, %0:i32, implicit-def $arguments
+    RETURN implicit-def $arguments
+
+  ; CHECK:      %0:i32 = CONST_I32 1, {{.*}}, debug-location !DILocation(line: 10
+  ; CHECK-NEXT: CALL @use
+...
+
+---
+# Cloning within the same BB preserves the debug location.
+# CHECK-LABEL: name: clone_same_bb
+name: clone_same_bb
+liveins:
+  - { reg: '$arguments' }
+tracksRegLiveness: true
+body: |
+  bb.0:
+    liveins: $arguments
+    %0:i32 = CONST_I32 1, implicit-def $arguments, debug-location !DILocation(line:10, scope:!6)
+    NOP implicit-def $arguments
+    CALL @use, %0:i32, implicit-def $arguments
+    CALL @use, %0:i32, implicit-def $arguments
+    RETURN implicit-def $arguments
+
+  ; CHECK:      CALL @use
+  ; CHECK-NEXT: %1:i32 = CONST_I32 1, {{.*}}, debug-location !DILocation(line: 10
+  ; CHECK-NEXT: CALL @use
+...
+
+---
+# Cloning to a different BB preserves the debug location in this case because
+# the destination BB has an instruction that has the same debug location
+# (test.c:10).
+# CHECK-LABEL: name: clone_different_bb_0
+name: clone_different_bb_0
+liveins:
+  - { reg: '$arguments' }
+tracksRegLiveness: true
+body: |
+  bb.0:
+    successors: %bb.1
+    liveins: $arguments
+    %0:i32 = CONST_I32 1, implicit-def $arguments, debug-location !DILocation(line:10, scope:!6)
+    BR %bb.1, implicit-def $arguments
+
+  bb.1:
+  ; predecessors: %bb.0
+    CALL @use, %0:i32, implicit-def $arguments, debug-location !DILocation(line:10, scope:!6)
+    RETURN implicit-def $arguments
+
+  ; CHECK: bb.1:
+  ; CHECK:      %1:i32 = CONST_I32 1, {{.*}}, debug-location !DILocation(line: 10
+  ; CHECK-NEXT: CALL @use, %1, {{.*}}, debug-location !DILocation(line: 10
+...
+
+---
+# Cloning to a different BB does NOT preserve the debug location in this case
+# because the destination BB doesn't have an instruction that has the same debug
+# location (It has test.c:20 but not test.c:10).
+# CHECK-LABEL: name: clone_different_bb_1
+name: clone_different_bb_1
+liveins:
+  - { reg: '$arguments' }
+tracksRegLiveness: true
+body: |
+  bb.0:
+    successors: %bb.1
+    liveins: $arguments
+    %0:i32 = CONST_I32 1, implicit-def $arguments, debug-location !DILocation(line:10, scope:!6)
+    BR %bb.1, implicit-def $arguments
+
+  bb.1:
+  ; predecessors: %bb.0
+    CALL @use, %0:i32, implicit-def $arguments, debug-location !DILocation(line:20, scope:!6)
+    RETURN implicit-def $arguments
+
+  ; CHECK: bb.1:
+  ; CHECK:      %1:i32 = CONST_I32 1
+  ; CHECK-NOT:  %1:i32 = CONST_I32 1, {{.*}}, debug-location !DILocation(line: 10
+  ; CHECK-NEXT: CALL @use, %1, {{.*}}, debug-location !DILocation(line: 20
+...