[mir-strip-debug] Optionally preserve debug info that wasn't from debugify/mir-debugify

[dsanders]

Summary

A few tests start out with debug info and expect it to reach
the output. For these tests we shouldn't strip the debug info

[aprantl]

llvm/lib/CodeGen/MachineStripDebug.cpp

36

Stripping only debug info added by the debugify pass.?

[vsk]

llvm/lib/CodeGen/MachineStripDebug.cpp

108

I think the default value for OnlyDebugified should come from a cl::opt (e.g. -mir-strip-debugify-only=0|1). Otherwise, changing the behavior of -mir-strip-debug would require further compiler changes.

[dsanders]

llvm/lib/CodeGen/MachineStripDebug.cpp

36

That sounds like it's stripping debug info when it's not stripping it.
Not stripping debug info (debugify metadata not found)?

108

That makes sense to me

[dsanders]

Option-controlled default
Improve message when declining to strip debug info

[vsk]

Looks good! I'll send a follow up change so we can share some of the stripping logic with the IR-level debugify pass.

llvm/lib/CodeGen/MachineStripDebug.cpp

36

Sgtm.

llvm/include/llvm/CodeGen/Passes.h

/// MachineDominanaceFrontier - This pass is a machine dominators analysis pass.
 
   /// Create IR Type Promotion pass. \see TypePromotion.cpp
   FunctionPass *createTypePromotionPass();
 
   /// Creates MIR Debugify pass. \see MachineDebugify.cpp
   ModulePass *createDebugifyMachineModulePass();
 
   /// Creates MIR Strip Debug pass. \see MachineStripDebug.cpp
-  ModulePass *createStripDebugMachineModulePass();
+  /// If OnlyDebugified is true then it will only strip debug info if it was
+  /// added by a Debugify pass. The module will be left unchanged if the debug
+  /// info was generated by another source such as clang.
+  ModulePass *createStripDebugMachineModulePass(bool OnlyDebugified);
 
   /// The pass fixups statepoint machine instruction to replace usage of
   /// caller saved registers with stack slots.
   extern char &FixupStatepointCallerSavedID;
 } // End llvm namespace
 
 #endif

llvm/lib/CodeGen/MachineStripDebug.cpp

 /// tests can be debugified without affecting the output MIR.
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/IR/DebugInfo.h"
 #include "llvm/InitializePasses.h"
+#include "llvm/Support/CommandLine.h"
 
 #define DEBUG_TYPE "mir-strip-debug"
 
 using namespace llvm;
 
 namespace {
+cl::opt<bool>
+    OnlyDebugifiedDefault("mir-strip-debugify-only",
+                          cl::desc("Should mir-strip-debug only strip debug "
+                                   "info from debugified modules by default"),
+                          cl::init(true));
 
 struct StripDebugMachineModule : public ModulePass {
   bool runOnModule(Module &M) override {
+    if (OnlyDebugified) {
+      NamedMDNode *DebugifyMD = M.getNamedMetadata("llvm.debugify");
+      if (!DebugifyMD) {
+        LLVM_DEBUG(dbgs() << "Not stripping debug info"
+                             " (debugify metadata not found)?\n");
+        return false;
+      }
+    }
+
     MachineModuleInfo &MMI =
         getAnalysis<MachineModuleInfoWrapperPass>().getMMI();
 
     bool Changed = false;
     for (Function &F : M.functions()) {
       MachineFunction &MF = MMI.getOrCreateMachineFunction(F);
       for (MachineBasicBlock &MBB : MF) {
         for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
if (NMD) {
       // If we left it empty we might as well remove it.
       if (NMD->getNumOperands() == 0)
         NMD->eraseFromParent();
     }
 
     return Changed;
   }
 
-  StripDebugMachineModule() : ModulePass(ID) {}
+  StripDebugMachineModule() : StripDebugMachineModule(OnlyDebugifiedDefault) {}
+  StripDebugMachineModule(bool OnlyDebugified)
+      : ModulePass(ID), OnlyDebugified(OnlyDebugified) {}
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<MachineModuleInfoWrapperPass>();
     AU.addPreserved<MachineModuleInfoWrapperPass>();
   }
 
   static char ID; // Pass identification.
+
+protected:
+  bool OnlyDebugified;
 };
 char StripDebugMachineModule::ID = 0;
 
 } // end anonymous namespace
 
 INITIALIZE_PASS_BEGIN(StripDebugMachineModule, DEBUG_TYPE,
                       "Machine Strip Debug Module", false, false)
 INITIALIZE_PASS_END(StripDebugMachineModule, DEBUG_TYPE,
                     "Machine Strip Debug Module", false, false)
 
-ModulePass *createStripDebugMachineModulePass() {
-  return new StripDebugMachineModule();
+ModulePass *createStripDebugMachineModulePass(bool OnlyDebugified) {
+  return new StripDebugMachineModule(OnlyDebugified);
 }

llvm/test/CodeGen/Generic/MIRStripDebug/dont-strip-real-debug-info.mir

+# RUN: llc -run-pass=mir-strip-debug -o - %s | FileCheck %s
+# RUN: llc -run-pass=mir-strip-debug,mir-debugify,mir-strip-debug -o - %s | FileCheck %s
+--- |
+  ; ModuleID = 'loc-only.ll'
+  source_filename = "loc-only.ll"
+  
+  define i32 @test(i32 %a, i32 %b) !dbg !4 {
+    %add = add i32 %a, 2, !dbg !10
+    call void @llvm.dbg.value(metadata i32 %add, metadata !7, metadata !DIExpression()), !dbg !10
+    %sub = sub i32 %add, %b, !dbg !11
+    call void @llvm.dbg.value(metadata i32 %sub, metadata !9, metadata !DIExpression()), !dbg !11
+    ret i32 %sub, !dbg !12
+  }
+  ; CHECK-LABEL: define i32 @test(i32 %a, i32 %b) !dbg !4 {
+  ; CHECK-NEXT:    %add = add i32 %a, 2, !dbg !10
+  ; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 %add, metadata !7, metadata !DIExpression()), !dbg !10
+  ; CHECK-NEXT:    %sub = sub i32 %add, %b, !dbg !11
+  ; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 %sub, metadata !9, metadata !DIExpression()), !dbg !11
+  ; CHECK-NEXT:    ret i32 %sub, !dbg !12
+  ; CHECK-NEXT:  }
+  
+  ; Function Attrs: nounwind readnone speculatable willreturn
+  declare void @llvm.dbg.value(metadata, metadata, metadata) #0
+  
+  ; Function Attrs: nounwind
+  declare void @llvm.stackprotector(i8*, i8**) #1
+  
+  attributes #0 = { nounwind readnone speculatable willreturn }
+  attributes #1 = { nounwind }
+  
+  !llvm.dbg.cu = !{!0}
+  ; CHECK: !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!3}
+  ; CHECK: !llvm.module.flags = !{!3}
+  
+  !0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+  !1 = !DIFile(filename: "<stdin>", directory: "/")
+  !2 = !{}
+  !3 = !{i32 2, !"Debug Info Version", i32 3}
+  !4 = distinct !DISubprogram(name: "test", linkageName: "test", scope: null, file: !1, line: 1, type: !5, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !6)
+  !5 = !DISubroutineType(types: !2)
+  !6 = !{!7, !9}
+  !7 = !DILocalVariable(name: "1", scope: !4, file: !1, line: 1, type: !8)
+  !8 = !DIBasicType(name: "ty32", size: 32, encoding: DW_ATE_unsigned)
+  !9 = !DILocalVariable(name: "2", scope: !4, file: !1, line: 2, type: !8)
+  !10 = !DILocation(line: 1, column: 1, scope: !4)
+  !11 = !DILocation(line: 2, column: 1, scope: !4)
+  !12 = !DILocation(line: 3, column: 1, scope: !4)
+
+  ; CHECK: !0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+  ; CHECK: !1 = !DIFile(filename: "<stdin>", directory: "/")
+  ; CHECK: !2 = !{}
+  ; CHECK: !3 = !{i32 2, !"Debug Info Version", i32 3}
+  ; CHECK: !4 = distinct !DISubprogram(name: "test", linkageName: "test", scope: null, file: !1, line: 1, type: !5, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !6)
+  ; CHECK: !5 = !DISubroutineType(types: !2)
+  ; CHECK: !6 = !{!7, !9}
+  ; CHECK: !7 = !DILocalVariable(name: "1", scope: !4, file: !1, line: 1, type: !8)
+  ; CHECK: !8 = !DIBasicType(name: "ty32", size: 32, encoding: DW_ATE_unsigned)
+  ; CHECK: !9 = !DILocalVariable(name: "2", scope: !4, file: !1, line: 2, type: !8)
+  ; CHECK: !10 = !DILocation(line: 1, column: 1, scope: !4)
+  ; CHECK: !11 = !DILocation(line: 2, column: 1, scope: !4)
+  ; CHECK: !12 = !DILocation(line: 3, column: 1, scope: !4)
+
+...
+---
+name:            test
+body:             |
+  bb.1 (%ir-block.0):
+    %0:_(s32) = G_IMPLICIT_DEF
+    %1:_(s32) = G_IMPLICIT_DEF
+    %2:_(s32) = G_CONSTANT i32 2, debug-location !DILocation(line: 0, scope: !4)
+    %3:_(s32) = G_ADD %0, %2, debug-location !10
+    DBG_VALUE %3(s32), $noreg, !7, !DIExpression(), debug-location !10
+    %4:_(s32) = G_SUB %3, %1, debug-location !11
+    DBG_VALUE %4(s32), $noreg, !9, !DIExpression(), debug-location !11
+
+    ; CHECK-LABEL: body:
+    ; CHECK-NEXT:    bb
+    ; CHECK-NEXT:      %0:_(s32) = G_IMPLICIT_DEF{{$}}
+    ; CHECK-NEXT:      %1:_(s32) = G_IMPLICIT_DEF{{$}}
+    ; CHECK-NEXT:      %2:_(s32) = G_CONSTANT i32 2, debug-location !DILocation(line: 0, scope: !4)
+    ; CHECK-NEXT:      %3:_(s32) = G_ADD %0, %2, debug-location !10
+    ; CHECK-NEXT:      DBG_VALUE %3(s32), $noreg, !7, !DIExpression(), debug-location !10
+    ; CHECK-NEXT:      %4:_(s32) = G_SUB %3, %1, debug-location !11
+    ; CHECK-NEXT:      DBG_VALUE %4(s32), $noreg, !9, !DIExpression(), debug-location !11
+...