Recommit r288212: Emit 'no line' information for interesting 'orphan' instructions.

DWARF specifies that "line 0" really means "no appropriate source
location" in the line table.  By default, use this for branch targets
and some other cases that have no specified source location, to
prevent inheriting unfortunate line numbers from physically preceding
instructions (which might be from completely unrelated source).

Updated patch allows enabling or suppressing this behavior for all
unspecified source locations.

Differential Revision: http://reviews.llvm.org/D24180

llvm-svn: 289468

lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp

@@ -200,8 +200,10 @@ void DebugHandlerBase::endInstruction() {
   assert(CurMI != nullptr);
   // Don't create a new label after DBG_VALUE instructions.
   // They don't generate code.
-  if (!CurMI->isDebugValue())
+  if (!CurMI->isDebugValue()) {
     PrevLabel = nullptr;
+    PrevInstBB = CurMI->getParent();
+  }
 
   DenseMap<const MachineInstr *, MCSymbol *>::iterator I =
       LabelsAfterInsn.find(CurMI);

lib/CodeGen/AsmPrinter/DebugHandlerBase.h

@@ -38,10 +38,12 @@ protected:
   MachineModuleInfo *MMI;
 
   /// Previous instruction's location information. This is used to
-  /// determine label location to indicate scope boundries in dwarf
+  /// determine label location to indicate scope boundaries in debug info.
-  /// debug info.
+  /// We track the previous instruction's source location (if not line 0),
+  /// whether it was a label, and its parent BB.
   DebugLoc PrevInstLoc;
   MCSymbol *PrevLabel = nullptr;
+  const MachineBasicBlock *PrevInstBB = nullptr;
 
   /// This location indicates end of function prologue and beginning of
   /// function body.

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -62,11 +62,6 @@ static cl::opt<bool>
 DisableDebugInfoPrinting("disable-debug-info-print", cl::Hidden,
                          cl::desc("Disable debug info printing"));
 
-static cl::opt<bool> UnknownLocations(
-    "use-unknown-locations", cl::Hidden,
-    cl::desc("Make an absence of debug location information explicit."),
-    cl::init(false));
-
 static cl::opt<bool>
 GenerateGnuPubSections("generate-gnu-dwarf-pub-sections", cl::Hidden,
                        cl::desc("Generate GNU-style pubnames and pubtypes"),
@@ -81,6 +76,13 @@ namespace {
 enum DefaultOnOff { Default, Enable, Disable };
 }
 
+static cl::opt<DefaultOnOff> UnknownLocations(
+    "use-unknown-locations", cl::Hidden,
+    cl::desc("Make an absence of debug location information explicit."),
+    cl::values(clEnumVal(Default, "At top of block or after label"),
+               clEnumVal(Enable, "In all cases"), clEnumVal(Disable, "Never")),
+    cl::init(Default));
+
 static cl::opt<DefaultOnOff>
 DwarfAccelTables("dwarf-accel-tables", cl::Hidden,
                  cl::desc("Output prototype dwarf accelerator tables."),
@@ -1010,31 +1012,73 @@ void DwarfDebug::beginInstruction(const MachineInstr *MI) {
   if (MI->isDebugValue() || MI->isCFIInstruction())
     return;
   const DebugLoc &DL = MI->getDebugLoc();
-  if (DL == PrevInstLoc)
+  // When we emit a line-0 record, we don't update PrevInstLoc; so look at
-    return;
+  // the last line number actually emitted, to see if it was line 0.
+  unsigned LastAsmLine =
+      Asm->OutStreamer->getContext().getCurrentDwarfLoc().getLine();
 
-  if (!DL) {
+  if (DL == PrevInstLoc) {
-    // We have an unspecified location, which might want to be line 0.
+    // If we have an ongoing unspecified location, nothing to do here.
-    if (UnknownLocations) {
+    if (!DL)
-      PrevInstLoc = DL;
+      return;
-      recordSourceLine(0, 0, nullptr, 0);
+    // We have an explicit location, same as the previous location.
+    // But we might be coming back to it after a line 0 record.
+    if (LastAsmLine == 0 && DL.getLine() != 0) {
+      // Reinstate the source location but not marked as a statement.
+      const MDNode *Scope = DL.getScope();
+      recordSourceLine(DL.getLine(), DL.getCol(), Scope, /*Flags=*/0);
     }
     return;
   }
 
-  // We have a new, explicit location.
+  if (!DL) {
+    // We have an unspecified location, which might want to be line 0.
+    // If we have already emitted a line-0 record, don't repeat it.
+    if (LastAsmLine == 0)
+      return;
+    // If user said Don't Do That, don't do that.
+    if (UnknownLocations == Disable)
+      return;
+    // See if we have a reason to emit a line-0 record now.
+    // Reasons to emit a line-0 record include:
+    // - User asked for it (UnknownLocations).
+    // - Instruction has a label, so it's referenced from somewhere else,
+    //   possibly debug information; we want it to have a source location.
+    // - Instruction is at the top of a block; we don't want to inherit the
+    //   location from the physically previous (maybe unrelated) block.
+    if (UnknownLocations == Enable || PrevLabel ||
+        (PrevInstBB && PrevInstBB != MI->getParent())) {
+      // Preserve the file number, if we can, to save space in the line table.
+      // Do not update PrevInstLoc, it remembers the last non-0 line.
+      // FIXME: Also preserve the column number, to save more space?
+      const MDNode *Scope = PrevInstLoc ? PrevInstLoc.getScope() : nullptr;
+      recordSourceLine(0, 0, Scope, 0);
+    }
+    return;
+  }
+
+  // We have an explicit location, different from the previous location.
+  // Don't repeat a line-0 record, but otherwise emit the new location.
+  // (The new location might be an explicit line 0, which we do emit.)
+  if (DL.getLine() == 0 && LastAsmLine == 0)
+    return;
   unsigned Flags = 0;
-  PrevInstLoc = DL;
   if (DL == PrologEndLoc) {
     Flags |= DWARF2_FLAG_PROLOGUE_END | DWARF2_FLAG_IS_STMT;
     PrologEndLoc = DebugLoc();
   }
-  if (DL.getLine() !=
+  // If the line changed, we call that a new statement; unless we went to
-      Asm->OutStreamer->getContext().getCurrentDwarfLoc().getLine())
+  // line 0 and came back, in which case it is not a new statement.
+  unsigned OldLine = PrevInstLoc ? PrevInstLoc.getLine() : LastAsmLine;
+  if (DL.getLine() && DL.getLine() != OldLine)
     Flags |= DWARF2_FLAG_IS_STMT;
 
   const MDNode *Scope = DL.getScope();
   recordSourceLine(DL.getLine(), DL.getCol(), Scope, Flags);
+
+  // If we're not at line 0, remember this location.
+  if (DL.getLine())
+    PrevInstLoc = DL;
 }
 
 static DebugLoc findPrologueEndLoc(const MachineFunction *MF) {

test/CodeGen/X86/stack-protector.ll

@@ -3888,23 +3888,27 @@ entry:
 define void @test32() #1 !dbg !7 {
 entry:
 ; LINUX-I386-LABEL: test32:
-; LINUX-I386:       .loc 1 0 0 prologue_end
+; LINUX-I386:       .loc 1 4 2 prologue_end
+; LINUX-I386:       .loc 1 0 0
 ; LINUX-I386-NEXT:  calll __stack_chk_fail
 
 ; LINUX-X64-LABEL: test32:
-; LINUX-X64:       .loc 1 0 0 prologue_end
+; LINUX-X64:       .loc 1 4 2 prologue_end
+; LINUX-X64:       .loc 1 0 0
 ; LINUX-X64-NEXT:  callq __stack_chk_fail
 
 ; LINUX-KERNEL-X64-LABEL: test32:
-; LINUX-KERNEL-X64:       .loc 1 0 0 prologue_end
+; LINUX-KERNEL-X64:       .loc 1 4 2 prologue_end
+; LINUX-KERNEL-X64:       .loc 1 0 0
 ; LINUX-KERNEL-X64-NEXT:  callq __stack_chk_fail
 
 ; OPENBSD-AMD64-LABEL: test32:
-; OPENBSD-AMD64:       .loc 1 0 0 prologue_end
+; OPENBSD-AMD64:       .loc 1 4 2 prologue_end
+; OPENBSD-AMD64:       .loc 1 0 0
 ; OPENBSD-AMD64-NEXT:  movl
 ; OPENBSD-AMD64-NEXT:  callq __stack_smash_handler
   %0 = alloca [5 x i8], align 1
-  ret void
+  ret void, !dbg !9
 }
 
 declare double @testi_aux()
@@ -3940,3 +3944,4 @@ attributes #5 = { ssp "stack-protector-buffer-size"="6" }
 !6 = distinct !DISubprogram(name: "__stack_chk_fail", scope: !1, type: !8, unit: !0)
 !7 = distinct !DISubprogram(name: "test32", scope: !1, type: !8, unit: !0)
 !8 = !DISubroutineType(types: !2)
+!9 = !DILocation(line: 4, column: 2, scope: !7)

test/CodeGen/X86/unknown-location.ll

@@ -1,4 +1,4 @@
-; RUN: llc < %s -asm-verbose=false -mtriple=x86_64-apple-darwin10 -use-unknown-locations | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -mtriple=x86_64-apple-darwin10 -use-unknown-locations=Enable | FileCheck %s
 
 ; The divide instruction does not have a debug location. CodeGen should
 ; represent this in the debug information. This is done by setting line

test/DebugInfo/AArch64/line-header.ll

@@ -3,4 +3,4 @@
 
 ; check line table length is correctly calculated for both big and little endian
 CHECK-LABEL: .debug_line contents:
-CHECK: total_length: 0x0000003c
+CHECK: total_length: 0x0000003e

test/DebugInfo/MIR/X86/no-cfi-loc.mir

@@ -1,6 +1,6 @@
 # Verify that a CFI instruction with no debug location
 # does not result in a line-0 location in the assembler.
-# RUN: %llc_dwarf -start-after=prologepilog -march=x86-64 -use-unknown-locations %s -o - | FileCheck %s
+# RUN: %llc_dwarf -start-after=prologepilog -march=x86-64 -use-unknown-locations=Enable %s -o - | FileCheck %s
 #
 # CHECK-NOT: .loc 1 0
 # CHECK:     .cfi_def_cfa_offset

test/DebugInfo/X86/dwarf-no-source-loc.ll

@@ -0,0 +1,77 @@
+; Verify "no source location" directives appear in appropriate places,
+; but don't appear when we explicitly suppress them.
+; RUN: llc < %s -o - | FileCheck %s
+; RUN: llc < %s -o - -use-unknown-locations=Disable | FileCheck %s --check-prefix=DISABLE
+
+; Generated from this .cpp targeting linux using -g
+; and then removed function attributes as clutter.
+;
+; void bar(int *);
+; void baz(int *);
+; # 5 "no-source-loc.cpp"
+; void foo(int x) {
+;   int z;
+;   if (x)
+; # 20 "include.h"
+;     bar(&z);
+; # 10 "no-source-loc.cpp"
+;   baz(&z);
+; }
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: uwtable
+define void @_Z3fooi(i32 %x) !dbg !6 {
+entry:
+  %x.addr = alloca i32, align 4
+  %z = alloca i32, align 4
+  store i32 %x, i32* %x.addr, align 4
+  %0 = load i32, i32* %x.addr, align 4, !dbg !8
+  %tobool = icmp ne i32 %0, 0, !dbg !8
+  br i1 %tobool, label %if.then, label %if.end, !dbg !8
+
+if.then:                                          ; preds = %entry
+  call void @_Z3barPi(i32* %z), !dbg !9
+  br label %if.end, !dbg !9
+
+if.end:                                           ; preds = %if.then, %entry
+  call void @_Z3bazPi(i32* %z), !dbg !12
+  ret void, !dbg !14
+}
+
+; CHECK:      .loc 1 7 7
+; CHECK-NOT:  .loc
+; CHECK:      .loc 1 0 0 is_stmt 0
+; CHECK-NOT:  .loc
+; CHECK:      .loc 2 20 5 is_stmt 1
+; CHECK:      .LBB0_2:
+; CHECK-NEXT: .loc 2 0 0 is_stmt 0
+; CHECK-NOT:  .loc
+; CHECK:      .loc 1 10 3 is_stmt 1
+;
+; DISABLE-NOT: .loc 1 0
+
+declare void @_Z3barPi(i32*)
+
+declare void @_Z3bazPi(i32*)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+!llvm.ident = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 4.0.0 (trunk 278782)", isOptimized: false, runtimeVersion: 0, emissionKind: LineTablesOnly, enums: !2)
+!1 = !DIFile(filename: "no-source-loc.cpp", directory: "/tests")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{!"clang version 4.0.0 (trunk 278782)"}
+!6 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 5, type: !7, isLocal: false, isDefinition: true, scopeLine: 5, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!7 = !DISubroutineType(types: !2)
+!8 = !DILocation(line: 7, column: 7, scope: !6)
+!9 = !DILocation(line: 20, column: 5, scope: !10)
+!10 = !DILexicalBlockFile(scope: !6, file: !11, discriminator: 0)
+!11 = !DIFile(filename: "include.h", directory: "/tests")
+!12 = !DILocation(line: 10, column: 3, scope: !13)
+!13 = !DILexicalBlockFile(scope: !6, file: !1, discriminator: 0)
+!14 = !DILocation(line: 11, column: 1, scope: !13)

test/DebugInfo/X86/tail-merge.ll

@@ -1,4 +1,4 @@
-; RUN: llc %s -mtriple=x86_64-unknown-unknown -use-unknown-locations=true -o - | FileCheck %s
+; RUN: llc %s -mtriple=x86_64-unknown-unknown -use-unknown-locations=Enable -o - | FileCheck %s
 
 ; Generated with "clang -gline-tables-only -c -emit-llvm -o - | opt -sroa -S"
 ; from source: