[DebugInfo] Allow DISubrange/DIGenericSubrange without count/upperBound. (#96474)

Due to the current order of metadata in DISubprgram, `Type` is processed
before `Unit` by the Verifier. This can cause a race and
 use of garbage data. Consider the following code:

```
int test(int a[][5])
{
    return a[0][2];
}
```

when compiled with clang, the control reaches
`Verifier::visitDISubrange` first with `CurrentSourceLang` still equal
to dwarf::DW_LANG_lo_user (32768). The `Verifier::visitDICompileUnit`
which sets the value of `CurrentSourceLang` is reached later. So
`Verifier::visitDISubrange` ends up using a wrong value of
`CurrentSourceLang`.

This behavior does not effect C like language much but is a problem for
Fortran. There is special processing in `Verifier::visitDISubrange` when
`CurrentSourceLang` is Fortran. With this problem, that special handling
is missed and verifier fails for any code that has Fortran's assumed
size array in a global subroutine.

Various solutions were tried to solve this problem before it was decided that
best course of action is to remove these checks from Verifier.

Author: abidh

llvm/lib/IR/Verifier.cpp

@@ -359,9 +359,6 @@ class Verifier : public InstVisitor<Verifier>, VerifierSupport {
   /// Whether the current function has a DISubprogram attached to it.
   bool HasDebugInfo = false;
 
-  /// The current source language.
-  dwarf::SourceLanguage CurrentSourceLang = dwarf::DW_LANG_lo_user;
-
   /// Stores the count of how many objects were passed to llvm.localescape for a
   /// given function and the largest index passed to llvm.localrecover.
   DenseMap<Function *, std::pair<unsigned, unsigned>> FrameEscapeInfo;
@@ -1156,10 +1153,6 @@ void Verifier::visitDIScope(const DIScope &N) {
 
 void Verifier::visitDISubrange(const DISubrange &N) {
   CheckDI(N.getTag() == dwarf::DW_TAG_subrange_type, "invalid tag", &N);
-  bool HasAssumedSizedArraySupport = dwarf::isFortran(CurrentSourceLang);
-  CheckDI(HasAssumedSizedArraySupport || N.getRawCountNode() ||
-              N.getRawUpperBound(),
-          "Subrange must contain count or upperBound", &N);
   CheckDI(!N.getRawCountNode() || !N.getRawUpperBound(),
           "Subrange can have any one of count or upperBound", &N);
   auto *CBound = N.getRawCountNode();
@@ -1188,8 +1181,6 @@ void Verifier::visitDISubrange(const DISubrange &N) {
 
 void Verifier::visitDIGenericSubrange(const DIGenericSubrange &N) {
   CheckDI(N.getTag() == dwarf::DW_TAG_generic_subrange, "invalid tag", &N);
-  CheckDI(N.getRawCountNode() || N.getRawUpperBound(),
-          "GenericSubrange must contain count or upperBound", &N);
   CheckDI(!N.getRawCountNode() || !N.getRawUpperBound(),
           "GenericSubrange can have any one of count or upperBound", &N);
   auto *CBound = N.getRawCountNode();
@@ -1413,8 +1404,6 @@ void Verifier::visitDICompileUnit(const DICompileUnit &N) {
   CheckDI(!N.getFile()->getFilename().empty(), "invalid filename", &N,
           N.getFile());
 
-  CurrentSourceLang = (dwarf::SourceLanguage)N.getSourceLanguage();
-
   CheckDI((N.getEmissionKind() <= DICompileUnit::LastEmissionKind),
           "invalid emission kind", &N);
 

llvm/test/Assembler/invalid-disubrange-count-missing.ll

@@ -0,0 +1,40 @@
+; RUN: %llc_dwarf %s -filetype=obj -o - | llvm-dwarfdump - | FileCheck %s
+
+; ModuleID = 'test.ll'
+source_filename = "test.f90"
+
+!llvm.module.flags = !{!1}
+!llvm.dbg.cu = !{!2}
+
+!1 = !{i32 2, !"Debug Info Version", i32 3}
+!2 = distinct !DICompileUnit(language: DW_LANG_Fortran90, file: !3, emissionKind: FullDebug, retainedTypes: !5)
+!3 = !DIFile(filename: "test.f90", directory: "dir")
+!5 = !{!6, !10, !13}
+!6 = !DICompositeType(tag: DW_TAG_array_type, baseType: !7, elements: !8)
+!7 = !DIBasicType(name: "integer", size: 32, align: 32, encoding: DW_ATE_signed)
+!8 = !{!9}
+!9 = !DISubrange(lowerBound: 2, stride: 16)
+!10 = !DICompositeType(tag: DW_TAG_array_type, baseType: !7, elements: !11)
+!11 = !{!12}
+!12 = !DISubrange()
+!13 = !DICompositeType(tag: DW_TAG_array_type, baseType: !7, elements: !14)
+!14 = !{!15}
+!15 = !DIGenericSubrange(lowerBound: !16, stride: !17)
+!16 = !DIExpression(DW_OP_push_object_address, DW_OP_plus_uconst, 48, DW_OP_deref)
+!17 = !DIExpression(DW_OP_push_object_address, DW_OP_plus_uconst, 56, DW_OP_deref)
+
+; Test that debug info is generated correctly in the absence of 'count' and
+; 'upperBound' in DISubrange/DIGenericSubrange.
+
+; CHECK-LABEL: DW_TAG_subrange_type
+; CHECK-NEXT:   DW_AT_type
+; CHECK-NEXT:   DW_AT_lower_bound     (2)
+; CHECK-NEXT:   DW_AT_byte_stride     (16)
+
+; CHECK-LABEL: DW_TAG_subrange_type
+; CHECK-NEXT:   DW_AT_type
+
+; CHECK-LABEL: DW_TAG_generic_subrange
+; CHECK-NEXT:   DW_AT_type
+; CHECK-NEXT:   DW_AT_lower_bound     (DW_OP_push_object_address, DW_OP_plus_uconst 0x30, DW_OP_deref)
+; CHECK-NEXT:   DW_AT_byte_stride     (DW_OP_push_object_address, DW_OP_plus_uconst 0x38, DW_OP_deref)