DwarfDebug: Pick next location in case of missing location at block b…

…egin Context: Compiler generated instructions do not have a debug location assigned to them. However emitting 0-line records for all of them bloats the line tables for very little benefit so we usually avoid doing that. Not emitting anything will lead to the previous debug location getting applied to the locationless instructions. This is not desirable for block begin and after labels. Previously we would emit simply emit line-0 records in this case, this patch changes the behavior to do a forward search for a debug location in these cases before emitting a line-0 record to further reduce line table bloat. Inspired by the discussion in https://reviews.llvm.org/D52862 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@343874 91177308-0d34-0410-b5e6-96231b3b80d8
ROCm · Oct 5, 2018 · 2078575 · 2078575
1 parent 628b7f5
commit 2078575
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Showing 8 changed files with 157 additions and 52 deletions.
diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -1313,6 +1313,49 @@ void DwarfDebug::collectEntityInfo(DwarfCompileUnit &TheCU,
   }
 }
 
+static const DebugLoc &
+findNextDebugLoc(MachineBasicBlock::const_iterator MBBI,
+                 MachineBasicBlock::const_iterator MBBE) {
+  static DebugLoc NoLocation;
+  for ( ; MBBI != MBBE; ++MBBI) {
+    if (MBBI->isDebugInstr())
+      continue;
+    const DebugLoc &DL = MBBI->getDebugLoc();
+    if (DL)
+      return DL;
+  }
+  return NoLocation;
+}
+
+void DwarfDebug::emitDebugLoc(const DebugLoc &DL) {
+  unsigned LastAsmLine =
+      Asm->OutStreamer->getContext().getCurrentDwarfLoc().getLine();
+
+  // 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.)
+  unsigned Line = DL.getLine();
+  if (PrevInstLoc && Line == 0 && LastAsmLine == 0)
+    return;
+  unsigned Flags = 0;
+  if (DL == PrologEndLoc) {
+    Flags |= DWARF2_FLAG_PROLOGUE_END | DWARF2_FLAG_IS_STMT;
+    PrologEndLoc = DebugLoc();
+  }
+  // If the line changed, we call that a new statement; unless we went to
+  // line 0 and came back, in which case it is not a new statement.
+  unsigned OldLine = PrevInstLoc ? PrevInstLoc.getLine() : LastAsmLine;
+  if (Line && Line != OldLine)
+    Flags |= DWARF2_FLAG_IS_STMT;
+
+  const MDNode *Scope = DL.getScope();
+  recordSourceLine(Line, DL.getCol(), Scope, Flags);
+
+  // If we're not at line 0, remember this location.
+  if (Line)
+    PrevInstLoc = DL;
+}
+
 // Process beginning of an instruction.
 void DwarfDebug::beginInstruction(const MachineInstr *MI) {
   DebugHandlerBase::beginInstruction(MI);
@@ -1352,54 +1395,41 @@ void DwarfDebug::beginInstruction(const MachineInstr *MI) {
     // If we have already emitted a line-0 record, don't repeat it.
     if (LastAsmLine == 0)
       return;
+    // By default we emit nothing to avoid line table bloat. However at the
+    // beginning of a basic block or after a label it is undesirable to let
+    // the previous location unchanged. In these cases do a forward search for
+    // the next valid debug location.
+    if (UnknownLocations == Default) {
+      const MachineBasicBlock &MBB = *MI->getParent();
+      if (!PrevLabel && PrevInstBB == &MBB)
+        return;
+
+      const DebugLoc &NextDL = findNextDebugLoc(MI->getIterator(), MBB.end());
+      if (NextDL) {
+        emitDebugLoc(NextDL);
+        return;
+      }
+    }
+
+    // We should emit a line-0 record.
     // 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 and column numbers, if we can, to save space in
-      // the encoded line table.
-      // Do not update PrevInstLoc, it remembers the last non-0 line.
-      const MDNode *Scope = nullptr;
-      unsigned Column = 0;
-      if (PrevInstLoc) {
-        Scope = PrevInstLoc.getScope();
-        Column = PrevInstLoc.getCol();
-      }
-      recordSourceLine(/*Line=*/0, Column, Scope, /*Flags=*/0);
+    // Emit a line-0 record now.
+    // Preserve the file and column numbers, if we can, to save space in
+    // the encoded line table.
+    // Do not update PrevInstLoc, it remembers the last non-0 line.
+    const MDNode *Scope = nullptr;
+    unsigned Column = 0;
+    if (PrevInstLoc) {
+      Scope = PrevInstLoc.getScope();
+      Column = PrevInstLoc.getCol();
     }
+    recordSourceLine(/*Line=*/0, Column, Scope, /*Flags=*/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 (PrevInstLoc && DL.getLine() == 0 && LastAsmLine == 0)
-    return;
-  unsigned Flags = 0;
-  if (DL == PrologEndLoc) {
-    Flags |= DWARF2_FLAG_PROLOGUE_END | DWARF2_FLAG_IS_STMT;
-    PrologEndLoc = DebugLoc();
-  }
-  // If the line changed, we call that a new statement; unless we went to
-  // 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;
+  emitDebugLoc(DL);
 }
 
 static DebugLoc findPrologueEndLoc(const MachineFunction *MF) {

diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.h b/lib/CodeGen/AsmPrinter/DwarfDebug.h
@@ -719,6 +719,9 @@ class DwarfDebug : public DebugHandlerBase {
   bool tuneForLLDB() const { return DebuggerTuning == DebuggerKind::LLDB; }
   bool tuneForSCE() const { return DebuggerTuning == DebuggerKind::SCE; }
   /// @}
+
+private:
+  void emitDebugLoc(const DebugLoc &DL);
 };
 
 } // end namespace llvm

diff --git a/test/DebugInfo/AArch64/line-header.ll b/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: 0x0000003f
+CHECK: total_length: 0x0000003c
diff --git a/test/DebugInfo/ARM/single-constant-use-preserves-dbgloc.ll b/test/DebugInfo/ARM/single-constant-use-preserves-dbgloc.ll
@@ -31,11 +31,10 @@ if.then:                                          ; preds = %entry
 
 if.end:                                           ; preds = %entry
 ; Materialize the constant.
-; CHECK:      .loc    1 0
+; CHECK:      .loc    1 7 5
 ; CHECK-NEXT: mvn     r0, #0
 
 ; The backend performs the store to %retval first, for some reason.
-; CHECK-NEXT: .loc    1 7 5
 ; CHECK-NEXT: str     r0, [sp, #4]
   store i32 -1, i32* %x, align 4, !dbg !19
 

diff --git a/test/DebugInfo/Mips/delay-slot.ll b/test/DebugInfo/Mips/delay-slot.ll
@@ -16,7 +16,7 @@
 ; CHECK: 0x0000000000000004      2      0      1   0             0  is_stmt prologue_end
 ; CHECK: 0x0000000000000024      3      0      1   0             0  is_stmt
 ; CHECK: 0x0000000000000034      4      0      1   0             0  is_stmt
-; CHECK: 0x0000000000000048      5      0      1   0             0  is_stmt
+; CHECK: 0x0000000000000044      5      0      1   0             0  is_stmt
 ; CHECK: 0x0000000000000058      5      0      1   0             0  is_stmt end_sequence
 
 

diff --git a/test/DebugInfo/NVPTX/debug-info.ll b/test/DebugInfo/NVPTX/debug-info.ll
@@ -36,14 +36,14 @@
 ; CHECK: setp.ge.s32     %p{{.+}}, %r{{.+}}, %r{{.+}};
 ; CHECK: .loc [[DEBUG_INFO_CU]] 7 7
 ; CHECK: @%p{{.+}} bra   [[BB:.+]];
+; CHECK: .loc [[DEBUG_INFO_CU]] 8 13
 ; CHECK: ld.param.f32    %f{{.+}}, [{{.+}}];
 ; CHECK: ld.param.u64    %rd{{.+}}, [{{.+}}];
 ; CHECK: cvta.to.global.u64      %rd{{.+}}, %rd{{.+}};
 ; CHECK: ld.param.u64    %rd{{.+}}, [{{.+}}];
 ; CHECK: cvta.to.global.u64      %rd{{.+}}, %rd{{.+}};
 ; CHECK: mul.wide.u32    %rd{{.+}}, %r{{.+}}, 4;
 ; CHECK: add.s64         %rd{{.+}}, %rd{{.+}}, %rd{{.+}};
-; CHECK: .loc [[DEBUG_INFO_CU]] 8 13
 ; CHECK: ld.global.f32   %f{{.+}}, [%rd{{.+}}];
 ; CHECK: add.s64         %rd{{.+}}, %rd{{.+}}, %rd{{.+}};
 ; CHECK: .loc [[DEBUG_INFO_CU]] 8 19

diff --git a/test/DebugInfo/X86/dwarf-no-source-loc.ll b/test/DebugInfo/X86/dwarf-no-source-loc.ll
@@ -40,15 +40,14 @@ if.end:                                           ; preds = %if.then, %entry
   ret void, !dbg !14
 }
 
-; CHECK:      .loc 1 7 7
+; CHECK:      .loc 1 7 7 prologue_end
 ; CHECK-NOT:  .loc
-; CHECK:      .loc 1 0 7 is_stmt 0
+; CHECK:      # %bb.1
+; CHECK-NEXT: .file 2 "/tests/include.h"
+; CHECK-NEXT: .loc 2 20 5
 ; CHECK-NOT:  .loc
-; CHECK:      .loc 2 20 5 is_stmt 1
 ; CHECK:      .LBB0_2:
-; CHECK-NEXT: .loc 2 0 5 is_stmt 0
-; CHECK-NOT:  .loc
-; CHECK:      .loc 1 10 3 is_stmt 1
+; CHECK:      .loc 1 10 3
 ;
 ; DISABLE-NOT: .loc 1 0
 

diff --git a/test/DebugInfo/X86/dwarf-no-source-loc.mir b/test/DebugInfo/X86/dwarf-no-source-loc.mir
@@ -0,0 +1,74 @@
+# RUN: llc -o - %s -start-before=patchable-function -use-unknown-locations=Default | FileCheck %s --check-prefixes=CHECK,DEFAULT
+# RUN: llc -o - %s -start-before=patchable-function -use-unknown-locations=Enable | FileCheck %s --check-prefixes=CHECK,ENABLE
+# RUN: llc -o - %s -start-before=patchable-function -use-unknown-locations=Disable | FileCheck %s --check-prefixes=CHECK,DISABLE
+--- |
+  target triple = "x86_64--"
+
+  !0 = !DIFile(filename: "dwarf-no-source-loc.mir", directory: "/")
+  !1 = distinct !DICompileUnit(file: !0, language: DW_LANG_C, emissionKind: LineTablesOnly)
+  !2 = distinct !DISubprogram(name: "func", unit: !1)
+  !3 = !DILocation(line: 17, scope: !2)
+  !4 = !DILocation(line: 42, scope: !2)
+
+  !llvm.dbg.cu = !{!1}
+  !llvm.module.flags = !{!10, !11}
+  !10 = !{i32 2, !"Dwarf Version", i32 4}
+  !11 = !{i32 2, !"Debug Info Version", i32 3}
+
+  define void @func() !dbg !2 {
+    unreachable
+  }
+...
+---
+name: func
+body: |
+  bb.0:
+    NOOP
+    NOOP
+    $eax = MOV32ri 1, debug-location !3
+    ; CHECK-LABEL: bb.0
+    ; CHECK: nop
+    ; CHECK: nop
+    ; CHECK: .loc 1 17 0 prologue_end
+    ; CHECK: movl $1, %eax
+
+  bb.1:
+    NOOP
+    $ebx = MOV32ri 2, debug-location !4
+    ; CHECK-LABEL: bb.1
+    ; DEFAULT: .loc 1 42 0
+    ; ENABLE: .loc 1 0
+    ; DISABLE-NOT: .loc 1 0
+    ; CHECK: nop
+    ; ENABLE: .loc 1 42 0
+    ; CHECK: movl $2, %ebx
+
+  bb.2:
+    NOOP
+    ; CHECK-LABEL: bb.2
+    ; DEFAULT: .loc 1 0 0 is_stmt 0
+    ; ENABLE: .loc 1 0 0 is_stmt 0
+    ; DISABLE-NOT: .loc 1 0
+    ; CHECK: nop
+
+  bb.3:
+    NOOP
+    $ecx = MOV32ri 3, debug-location !3
+    ; CHECK-LABEL: bb.3
+    ; CHECK: nop
+    ; DEFAULT: .loc 1 17 0 is_stmt 1
+    ; ENABLE: .loc 1 17 0 is_stmt 1
+    ; DISABLE-NOT: .loc 1 0
+    ; CHECK: movl $3, %ecx
+
+  bb.4:
+    NOOP
+    $edx = MOV32ri 4, debug-location !4
+    ; CHECK: bb.4
+    ; DEFAULT: .loc 1 42 0
+    ; ENABLE: .loc 1 0 0 is_stmt 0
+    ; DISABLE-NOT: .loc 1 0
+    ; CHECK: nop
+    ; ENABLE: .loc 1 42 0 is_stmt 1
+    ; CHECK: movl $4, %edx
+...