[DebugInfo] Discard invalid DBG_VALUE instructions in LiveDebugVariables

Summary: This is a workaround for pr36417 https://bugs.llvm.org/show_bug.cgi?id=36417 LiveDebugVariables will now verify that the DBG_VALUE instructions are sane (prior to register allocation) by asking LIS if a virtual register used in the DBG_VALUE is live (or dead def) in the slot index before the DBG_VALUE. If it isn't sane the DBG_VALUE is discarded. One pass that was identified as introducing non-sane DBG_VALUE instructtons, when analysing pr36417, was the DAG->DAG Instruction Selection. It sometimes inserts DBG_VALUE instructions referring to a virtual register that is defined later in the same basic block. So it is a use before def kind of problem. The DBG_VALUE is typically inserted in the beginning of a basic block when this happens. The problem can be seen in the test case test/DebugInfo/X86/dbg-value-inlined-parameter.ll Reviewers: aprantl, rnk, probinson Reviewed By: aprantl Subscribers: vsk, davide, alexcrichton, Ka-Ka, eraman, llvm-commits, JDevlieghere Differential Revision: https://reviews.llvm.org/D43956 llvm-svn: 326769
llvm · Mar 6, 2018 · bdf0c00 · bdf0c00
1 parent 2f35873
commit bdf0c00
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Showing 3 changed files with 181 additions and 4 deletions.
diff --git a/llvm/lib/CodeGen/LiveDebugVariables.cpp b/llvm/lib/CodeGen/LiveDebugVariables.cpp
@@ -514,6 +514,39 @@ bool LDVImpl::handleDebugValue(MachineInstr &MI, SlotIndex Idx) {
     return false;
   }
 
+  // Detect invalid DBG_VALUE instructions, with a debug-use of a virtual
+  // register that hasn't been defined yet. If we do not remove those here, then
+  // the re-insertion of the DBG_VALUE instruction after register allocation
+  // will be incorrect.
+  // TODO: If earlier passes are corrected to generate sane debug information
+  // (and if the machine verifier is improved to catch this), then these checks
+  // could be removed or replaced by asserts.
+  bool Discard = false;
+  if (MI.getOperand(0).isReg() &&
+      TargetRegisterInfo::isVirtualRegister(MI.getOperand(0).getReg())) {
+    const unsigned Reg = MI.getOperand(0).getReg();
+    if (!LIS->hasInterval(Reg)) {
+      // The DBG_VALUE is described by a virtual register that does not have a
+      // live interval. Discard the DBG_VALUE.
+      Discard = true;
+      DEBUG(dbgs() << "Discarding debug info (no LIS interval): "
+            << Idx << " " << MI);
+    } else {
+      // The DBG_VALUE is only valid if either Reg is live out from Idx, or Reg
+      // is defined dead at Idx (where Idx is the slot index for the instruction
+      // preceeding the DBG_VALUE).
+      const LiveInterval &LI = LIS->getInterval(Reg);
+      LiveQueryResult LRQ = LI.Query(Idx);
+      if (!LRQ.valueOutOrDead()) {
+        // We have found a DBG_VALUE with the value in a virtual register that
+        // is not live. Discard the DBG_VALUE.
+        Discard = true;
+        DEBUG(dbgs() << "Discarding debug info (reg not live): "
+              << Idx << " " << MI);
+      }
+    }
+  }
+
   // Get or create the UserValue for (variable,offset) here.
   bool IsIndirect = MI.getOperand(1).isImm();
   if (IsIndirect)
@@ -522,7 +555,10 @@ bool LDVImpl::handleDebugValue(MachineInstr &MI, SlotIndex Idx) {
   const DIExpression *Expr = MI.getDebugExpression();
   UserValue *UV =
       getUserValue(Var, Expr, MI.getDebugLoc());
-  UV->addDef(Idx, MI.getOperand(0), IsIndirect);
+  if (!Discard)
+    UV->addDef(Idx, MI.getOperand(0), IsIndirect);
+  else
+    UV->addDef(Idx, MachineOperand::CreateReg(0U, RegState::Debug), false);
   return true;
 }
 

diff --git a/llvm/test/DebugInfo/X86/dbg-value-inlined-parameter.ll b/llvm/test/DebugInfo/X86/dbg-value-inlined-parameter.ll
@@ -32,10 +32,10 @@
 ;CHECK-NEXT: DW_AT_call_line
 
 ;CHECK: DW_TAG_formal_parameter
-;FIXME: Linux shouldn't drop this parameter either...
 ;CHECK-NOT: DW_TAG
-;DARWIN:   DW_AT_abstract_origin {{.*}} "sp"
-;DARWIN: DW_TAG_formal_parameter
+;FIXME: Shouldn't drop this parameter...
+;XCHECK:   DW_AT_abstract_origin {{.*}} "sp"
+;XCHECK: DW_TAG_formal_parameter
 ;CHECK: DW_AT_abstract_origin {{.*}} "nums"
 ;CHECK-NOT: DW_TAG_formal_parameter
 

diff --git a/llvm/test/DebugInfo/X86/live-debug-vars-discard-invalid.mir b/llvm/test/DebugInfo/X86/live-debug-vars-discard-invalid.mir
@@ -0,0 +1,141 @@
+# RUN: llc -mtriple=x86_64-linux-gnu -start-before greedy -stop-after virtregrewriter -o - %s | FileCheck %s
+
+--- |
+  ; ModuleID = '<stdin>'
+  source_filename = "test/DebugInfo/X86/dbg-value-inlined-parameter.ll"
+  target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+  target triple = "x86_64-apple-darwin"
+
+  %struct.S1 = type { float*, i32 }
+
+  @p = common global %struct.S1 zeroinitializer, align 8, !dbg !0
+
+  ; Function Attrs: nounwind optsize ssp
+  define void @foobar() !dbg !15 {
+  entry:
+    tail call void @llvm.dbg.value(metadata %struct.S1* @p, metadata !18, metadata !DIExpression()) , !dbg !25
+    ret void, !dbg !32
+  }
+
+  ; Function Attrs: nounwind readnone speculatable
+  declare void @llvm.dbg.value(metadata, metadata, metadata) #2
+
+  !llvm.dbg.cu = !{!2}
+  !llvm.module.flags = !{!14}
+
+  !0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+  !1 = !DIGlobalVariable(name: "p", scope: !2, file: !3, line: 14, type: !6, isLocal: false, isDefinition: true)
+  !2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 2.9 (trunk 125693)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, retainedTypes: !4, globals: !5, imports: !4)
+  !3 = !DIFile(filename: "nm2.c", directory: "/private/tmp")
+  !4 = !{}
+  !5 = !{!0}
+  !6 = !DIDerivedType(tag: DW_TAG_typedef, name: "S1", scope: !2, file: !3, line: 4, baseType: !7)
+  !7 = !DICompositeType(tag: DW_TAG_structure_type, name: "S1", scope: !2, file: !3, line: 1, size: 128, align: 64, elements: !8)
+  !8 = !{!9, !12}
+  !9 = !DIDerivedType(tag: DW_TAG_member, name: "m", scope: !3, file: !3, line: 2, baseType: !10, size: 64, align: 64)
+  !10 = !DIDerivedType(tag: DW_TAG_pointer_type, scope: !2, baseType: !11, size: 64, align: 64)
+  !11 = !DIBasicType(name: "float", size: 32, align: 32, encoding: DW_ATE_float)
+  !12 = !DIDerivedType(tag: DW_TAG_member, name: "nums", scope: !3, file: !3, line: 3, baseType: !13, size: 32, align: 32, offset: 64)
+  !13 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+  !14 = !{i32 1, !"Debug Info Version", i32 3}
+  !15 = distinct !DISubprogram(name: "foobar", scope: !3, file: !3, line: 15, type: !16, isLocal: false, isDefinition: true, virtualIndex: 6, isOptimized: true, unit: !2)
+  !16 = !DISubroutineType(types: !17)
+  !17 = !{null}
+  !18 = !DILocalVariable(name: "sp", arg: 1, scope: !19, file: !3, line: 7, type: !24)
+  !19 = distinct !DISubprogram(name: "foo", scope: !3, file: !3, line: 8, type: !20, isLocal: false, isDefinition: true, scopeLine: 8, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: true, unit: !2, variables: !22)
+  !20 = !DISubroutineType(types: !21)
+  !21 = !{!13}
+  !22 = !{!18, !23}
+  !23 = !DILocalVariable(name: "nums", arg: 2, scope: !19, file: !3, line: 7, type: !13)
+  !24 = !DIDerivedType(tag: DW_TAG_pointer_type, scope: !2, baseType: !6, size: 64, align: 64)
+  !25 = !DILocation(line: 7, column: 13, scope: !19, inlinedAt: !26)
+  !26 = !DILocation(line: 16, column: 3, scope: !27)
+  !27 = distinct !DILexicalBlock(scope: !15, file: !3, line: 15, column: 15)
+  !32 = !DILocation(line: 17, column: 1, scope: !27)
+
+...
+---
+name:            foobar
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    %1:gr64 = IMPLICIT_DEF
+    %2:gr64 = IMPLICIT_DEF
+
+  bb.1:
+    ; This DBG_VALUE will be discarded (use before def of %0).
+    DBG_VALUE debug-use %0, debug-use $noreg, !18, !DIExpression(), debug-location !25
+    %0:gr64 = IMPLICIT_DEF
+    %0:gr64 = IMPLICIT_DEF
+    %0:gr64 = IMPLICIT_DEF
+    %0:gr64 = IMPLICIT_DEF
+
+  bb.2:
+    ; This DBG_VALUE will be discarded (%1 is defined earlier, but it is not live in, so we do not know where %1 is stored).
+    DBG_VALUE debug-use %1, debug-use $noreg, !18, !DIExpression(), debug-location !25
+    %1:gr64 = IMPLICIT_DEF
+    %1:gr64 = IMPLICIT_DEF
+    %1:gr64 = IMPLICIT_DEF
+    %1:gr64 = IMPLICIT_DEF
+    ; This DBG_VALUE is kept, even if %1 is dead, it was defined in the prev instruction,
+    ; so the value should be available for as long as the register allocated to %1 is live.
+    DBG_VALUE debug-use %1, debug-use $noreg, !18, !DIExpression(), debug-location !25
+
+  bb.3:
+    %1:gr64 = IMPLICIT_DEF
+    DBG_VALUE 0, debug-use $noreg, !23, !DIExpression(), debug-location !25
+    ; This DBG_VALUE is kept, even if %1 is dead, it was defined in the prev non-dbg instruction,
+    ; so the value should be available for as long as the register allocated to %1 is live.
+    DBG_VALUE debug-use %1, debug-use $noreg, !18, !DIExpression(), debug-location !25
+
+  bb.4:
+    ; All DBG_VALUEs here should survive. %2 is livein as it was defined in bb.0, and it has use/def in the BTS64rr instruction.
+    DBG_VALUE debug-use %2, debug-use $noreg, !18, !DIExpression(), debug-location !25
+    %2:gr64 = BTS64rr %2, 0, implicit-def $eflags
+    DBG_VALUE 0, debug-use $noreg, !23, !DIExpression(), debug-location !25
+    DBG_VALUE debug-use %2, debug-use $noreg, !18, !DIExpression(), debug-location !25
+    %2:gr64 = BTS64rr %2, 0, implicit-def $eflags
+    DBG_VALUE debug-use %2, debug-use $noreg, !18, !DIExpression(), debug-location !25
+    %2:gr64 = BTS64rr %2, 0, implicit-def $eflags
+    DBG_VALUE debug-use %2, debug-use $noreg, !18, !DIExpression(), debug-location !25
+
+  bb.5:
+    RET 0, debug-location !32
+...
+
+# CHECK-LABEL: name: foobar
+
+# CHECK-LABEL: bb.1:
+## After solving https://bugs.llvm.org/show_bug.cgi?id=36579 we expect to get a
+##   DBG_VALUE debug-use $noreg
+## here.
+# CHECK-NOT:    DBG_VALUE
+
+# CHECK-LABEL: bb.2:
+## After solving https://bugs.llvm.org/show_bug.cgi?id=36579 we expect to get a
+##   DBG_VALUE debug-use $noreg
+## here.
+# CHECK-NOT:    DBG_VALUE
+# CHECK:        dead renamable $rcx = IMPLICIT_DEF
+# CHECK-NEXT:   dead renamable $rcx = IMPLICIT_DEF
+# CHECK-NEXT:   dead renamable $rcx = IMPLICIT_DEF
+# CHECK-NEXT:   dead renamable $rcx = IMPLICIT_DEF
+# CHECK-NEXT:   DBG_VALUE debug-use $rcx, debug-use $noreg, !18, !DIExpression()
+
+# CHECK-LABEL: bb.3:
+# CHECK:        dead renamable $rcx = IMPLICIT_DEF
+# CHECK-NEXT:   DBG_VALUE 0, debug-use $noreg, !23, !DIExpression()
+# CHECK-NEXT:   DBG_VALUE debug-use $rcx, debug-use $noreg, !18, !DIExpression()
+
+# CHECK-LABEL: bb.4:
+# CHECK:        liveins: $rax
+# CHECK:        DBG_VALUE debug-use $rax, debug-use $noreg, !18, !DIExpression()
+# CHECK-NEXT:   renamable $rax = BTS64rr killed renamable $rax, 0, implicit-def $eflags
+# CHECK-NEXT:   DBG_VALUE 0, debug-use $noreg, !23, !DIExpression()
+# CHECK-NEXT:   DBG_VALUE debug-use $rax, debug-use $noreg, !18, !DIExpression()
+# CHECK-NEXT:   renamable $rax = BTS64rr killed renamable $rax, 0, implicit-def $eflags
+# CHECK-NEXT:   DBG_VALUE debug-use $rax, debug-use $noreg, !18, !DIExpression()
+# CHECK-NEXT:   dead renamable $rax = BTS64rr killed renamable $rax, 0, implicit-def $eflags
+
+# CHECK-LABEL: bb.5:
+# CHECK-NEXT:   RET 0