[DebugInfo] Fix for DW_OP_LLVM_fragment in DIExpression::isImplicit()

DIExpression::isImplicit() did not handle DW_OP_LLVM_fragment
correctly. It was scanning the elements in the expression by
iterating from the end. But we do not know the position of
ops unless we iterate from the beginning of the expression,
since DW_OP:s and their operands are stored flat in the expression
list. The old code also assumed that a DW_OP_LLVM_fragment
only occupied one element in the expression list, but it actually
occupies three elements.

diff --git a/llvm/lib/IR/DebugInfoMetadata.cpp b/llvm/lib/IR/DebugInfoMetadata.cpp
index 94ec3ab..8ccd855 100644 (file)
--- a/llvm/lib/IR/DebugInfoMetadata.cpp
+++ b/llvm/lib/IR/DebugInfoMetadata.cpp
@@ -929,17 +929,22 @@ bool DIExpression::isValid() const {
 }
 
 bool DIExpression::isImplicit() const {
-  unsigned N = getNumElements();
-  if (isValid() && N > 0) {
-    switch (getElement(N-1)) {
-      case dwarf::DW_OP_stack_value:
-      case dwarf::DW_OP_LLVM_tag_offset:
-        return true;
-      case dwarf::DW_OP_LLVM_fragment:
-        return N > 1 && getElement(N-2) == dwarf::DW_OP_stack_value;
-      default: break;
+  if (!isValid())
+    return false;
+
+  if (getNumElements() == 0)
+    return false;
+
+  for (const auto &It : expr_ops()) {
+    switch (It.getOp()) {
+    default:
+      break;
+    case dwarf::DW_OP_stack_value:
+    case dwarf::DW_OP_LLVM_tag_offset:
+      return true;
     }
   }
+
   return false;
 }
 
@@ -1013,6 +1018,8 @@ bool DIExpression::extractIfOffset(int64_t &Offset) const {
 
 const DIExpression *DIExpression::extractAddressClass(const DIExpression *Expr,
                                                       unsigned &AddrClass) {
+  // FIXME: This seems fragile. Nothing that verifies that these elements
+  // actually map to ops and not operands.
   const unsigned PatternSize = 4;
   if (Expr->Elements.size() >= PatternSize &&
       Expr->Elements[PatternSize - 4] == dwarf::DW_OP_constu &&

diff --git a/llvm/test/CodeGen/X86/dbg-value-func-arg.ll b/llvm/test/CodeGen/X86/dbg-value-func-arg.ll
new file mode 100644 (file)
index 0000000..beaf848
--- /dev/null
+++ b/llvm/test/CodeGen/X86/dbg-value-func-arg.ll
@@ -0,0 +1,86 @@
+; RUN: llc < %s -mtriple i386-unknown-unknown -O1 -stop-before=finalize-isel | FileCheck %s
+
+; Test case is designed to show the differences related to how implicit values
+; are handled by SelectionDAGBuilder::EmitFuncArgumentDbgValue.
+;
+; One purpose is to validate a bugfix in DIExpression::isImplicit() related
+; to DIExpressions containing both DW_OP_stack_value and DW_OP_LLVM_fragment.
+;
+; IR generated by:
+;
+;   // clang -S -target i386-- -Wall -g -O1 -mllvm -stop-before=finalize-isel
+;
+;   typedef struct {
+;       int x;
+;       int *y;
+;   } bar;
+;
+;   bar* func1(bar *p1, long p2, bar p3)
+;   {
+;      bar *foo1 = p1+18;
+;      p3.y = &((p1+18)->x);
+;      return p1;
+;   }
+
+
+target datalayout = "e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-f64:32:64-f80:32-n8:16:32-S128"
+target triple = "i386-unknown-unknown"
+
+%struct.bar = type { i32, i32* }
+
+; Function Attrs: norecurse nounwind readnone
+define dso_local %struct.bar* @func1(%struct.bar* readnone returned %0, i32 %1, i32 %2, i32* nocapture readnone %3) local_unnamed_addr #0 !dbg !8 {
+; CHECK-DAG: DBG_VALUE %fixed-stack.1, $noreg, {{.*}}, !DIExpression(DW_OP_deref, DW_OP_LLVM_fragment, 0, 32),
+; CHECK-DAG: DBG_VALUE %fixed-stack.0, $noreg, {{.*}}, !DIExpression(DW_OP_deref, DW_OP_LLVM_fragment, 32, 32),
+; CHECK-DAG: DBG_VALUE %fixed-stack.3, $noreg, {{.*}}, !DIExpression(DW_OP_deref),
+; CHECK-DAG: DBG_VALUE %fixed-stack.2, $noreg, {{.*}}, !DIExpression(DW_OP_deref),
+; CHECK-DAG: DBG_VALUE %fixed-stack.3, $noreg, {{.*}}, !DIExpression(DW_OP_deref_size, 4, DW_OP_plus_uconst, 144, DW_OP_stack_value),
+; CHECK-DAG: DBG_VALUE %fixed-stack.3, $noreg, {{.*}}, !DIExpression(DW_OP_deref_size, 4, DW_OP_plus_uconst, 144, DW_OP_stack_value, DW_OP_LLVM_fragment, 32, 32),
+
+  call void @llvm.dbg.value(metadata i32 %2, metadata !24, metadata !DIExpression(DW_OP_LLVM_fragment, 0, 32)), !dbg !26
+  call void @llvm.dbg.value(metadata i32* %3, metadata !24, metadata !DIExpression(DW_OP_LLVM_fragment, 32, 32)), !dbg !26
+  call void @llvm.dbg.value(metadata %struct.bar* %0, metadata !22, metadata !DIExpression()), !dbg !26
+  call void @llvm.dbg.value(metadata i32 %1, metadata !23, metadata !DIExpression()), !dbg !26
+  call void @llvm.dbg.value(metadata %struct.bar* %0, metadata !25, metadata !DIExpression(DW_OP_plus_uconst, 144, DW_OP_stack_value)), !dbg !26
+  call void @llvm.dbg.value(metadata %struct.bar* %0, metadata !24, metadata !DIExpression(DW_OP_plus_uconst, 144, DW_OP_stack_value, DW_OP_LLVM_fragment, 32, 32)), !dbg !26
+  ret %struct.bar* %0, !dbg !27
+}
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #0 = { norecurse nounwind readnone }
+attributes #1 = { nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6}
+!llvm.ident = !{!7}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0 (trunk 375507)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "example.c", directory: "/home/ubuntu")
+!2 = !{}
+!3 = !{i32 1, !"NumRegisterParameters", i32 0}
+!4 = !{i32 2, !"Dwarf Version", i32 4}
+!5 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = !{i32 1, !"wchar_size", i32 4}
+!7 = !{!"clang version 10.0.0 (trunk 375507)"}
+!8 = distinct !DISubprogram(name: "func1", scope: !9, file: !9, line: 6, type: !10, scopeLine: 7, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !21)
+!9 = !DIFile(filename: "./example.c", directory: "/home/ubuntu")
+!10 = !DISubroutineType(types: !11)
+!11 = !{!12, !12, !20, !13}
+!12 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 32)
+!13 = !DIDerivedType(tag: DW_TAG_typedef, name: "bar", file: !9, line: 4, baseType: !14)
+!14 = distinct !DICompositeType(tag: DW_TAG_structure_type, file: !9, line: 1, size: 64, elements: !15)
+!15 = !{!16, !18}
+!16 = !DIDerivedType(tag: DW_TAG_member, name: "x", scope: !14, file: !9, line: 2, baseType: !17, size: 32)
+!17 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!18 = !DIDerivedType(tag: DW_TAG_member, name: "y", scope: !14, file: !9, line: 3, baseType: !19, size: 32, offset: 32)
+!19 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !17, size: 32)
+!20 = !DIBasicType(name: "long int", size: 32, encoding: DW_ATE_signed)
+!21 = !{!22, !23, !24, !25}
+!22 = !DILocalVariable(name: "p1", arg: 1, scope: !8, file: !9, line: 6, type: !12)
+!23 = !DILocalVariable(name: "p2", arg: 2, scope: !8, file: !9, line: 6, type: !20)
+!24 = !DILocalVariable(name: "p3", arg: 3, scope: !8, file: !9, line: 6, type: !13)
+!25 = !DILocalVariable(name: "foo1", scope: !8, file: !9, line: 8, type: !12)
+!26 = !DILocation(line: 0, scope: !8)
+!27 = !DILocation(line: 10, column: 4, scope: !8)