[DebugInfo] Support for DWARF operator DW_OP_over

[alok]

Summary

llvm rejects DWARF operator DW_OP_over.This DWARF
operator is needed for Flang to support assumed rank array.
Debugger in such cases calculates Array bounds using
DW_AT_rank and DW_TAG_generic_subrange.
for (i=0;i<rank;i++) {
lBound of i'th dim =>
Debugger keeps hidden operator DW_OP_lit"i" before lBound expression
and this operator is used by the expression having DW_OP_over.
}

Summary:

Currently llvm rejects DWARF operator DW_OP_over.
below error is produced when llvm finds this operator.

[..]
invalid expression
!DIExpression(151, 20, 16, 48, 30, 35, 80, 34, 6)
warning: ignoring invalid debug info in over.ll
[..]

There are some parts missing in support of this operator, need to
be completed.

Testing

-added a unit testcase
-check-debuginfo
-check-llvm

[alok]

Re-based,

[aprantl]

Can you add an assembler roundtrip test to test/Assembler to test the change to lib/IR?
It just can contain a single named node that holds a DIExpression.

[alok]

Updated to re-base and incorporate comment from @aprantl .

[alok]

In D89208#2325611, @aprantl wrote:

Can you add an assembler roundtrip test to test/Assembler to test the change to lib/IR?
It just can contain a single named node that holds a DIExpression.

Thanks for your comment and suggestion. It is included now.

[aprantl]

Thanks!

llvm/docs/LangRef.rst

- ``DW_OP_LLVM_entry_value, N`` can only appear at the beginning of a
   parameter.
 - ``DW_OP_breg`` (or ``DW_OP_bregx``) represents a content on the provided
   signed offset of the specified register. The opcode is only generated by the
   ``AsmPrinter`` pass to describe call site parameter value which requires an
   expression over two registers.
 - ``DW_OP_push_object_address`` pushes the address of the object which can then
   serve as a descriptor in subsequent calculation. This opcode can be used to
   calculate bounds of fortran allocatable array which has array descriptors.
+- ``DW_OP_over`` duplicates the entry currently second in the stack at the top
+  of the stack. This opcode can be used to calculate bounds of fortran assumed
+  rank array which has rank known at run time and current dimension number is
+  implicitly first element of the stack.
 
 DWARF specifies three kinds of simple location descriptions: Register, memory,
 and implicit location descriptions.  Note that a location description is
 defined over certain ranges of a program, i.e the location of a variable may
 change over the course of the program. Register and memory location
 descriptions describe the *concrete location* of a source variable (in the
 sense that a debugger might modify its value), whereas *implicit locations*
 describe merely the actual *value* of a source variable which might not exist

llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp

while (ExprCursor) {
     case dwarf::DW_OP_xor:
     case dwarf::DW_OP_shl:
     case dwarf::DW_OP_shr:
     case dwarf::DW_OP_shra:
     case dwarf::DW_OP_lit0:
     case dwarf::DW_OP_not:
     case dwarf::DW_OP_dup:
     case dwarf::DW_OP_push_object_address:
+    case dwarf::DW_OP_over:
       emitOp(OpNum);
       break;
     case dwarf::DW_OP_deref:
       assert(!isRegisterLocation());
       if (!isMemoryLocation() && ::isMemoryLocation(ExprCursor))
         // Turning this into a memory location description makes the deref
         // implicit.
         LocationKind = Memory;

llvm/lib/IR/DebugInfoMetadata.cpp

for (auto I = expr_op_begin(), E = expr_op_end(); I != E; ++I) {
     case dwarf::DW_OP_deref_size:
     case dwarf::DW_OP_xderef:
     case dwarf::DW_OP_lit0:
     case dwarf::DW_OP_not:
     case dwarf::DW_OP_dup:
     case dwarf::DW_OP_regx:
     case dwarf::DW_OP_bregx:
     case dwarf::DW_OP_push_object_address:
+    case dwarf::DW_OP_over:
       break;
     }
   }
   return true;
 }
 
 bool DIExpression::isImplicit() const {
   if (!isValid())

llvm/test/DebugInfo/X86/dwarfdump-over.ll

+; RUN: llc %s -filetype=obj -o %t.o
+; RUN: llvm-dwarfdump  %t.o | FileCheck %s
+
+; Test whether DW_OP_over is processed properly.
+; CHECK-LABEL:  DW_TAG_array_type
+; CHECK-LABEL:  DW_TAG_array_type
+; CHECK-NOT: DW_TAG
+; CHECK:     DW_AT_data_location
+; CHECK:     DW_AT_allocated
+; CHECK: DW_TAG_subrange_type
+; CHECK:  DW_AT_lower_bound     (DW_OP_push_object_address, DW_OP_over, DW_OP_constu 0x30, DW_OP_mul, DW_OP_plus_uconst 0x50, DW_OP_plus, DW_OP_deref)
+; CHECK:  DW_AT_upper_bound     (DW_OP_push_object_address, DW_OP_over, DW_OP_constu 0x30, DW_OP_mul, DW_OP_plus_uconst 0x78, DW_OP_plus, DW_OP_deref)
+; CHECK:  DW_AT_byte_stride     (DW_OP_push_object_address, DW_OP_over, DW_OP_constu 0x30, DW_OP_mul, DW_OP_plus_uconst 0x70, DW_OP_plus, DW_OP_deref, DW_OP_lit4, DW_OP_mul)
+; CHECK: DW_TAG_subrange_type
+; CHECK   DW_AT_lower_bound (DW_OP_push_object_address, DW_OP_plus_uconst 0x80, DW_OP_deref)
+; CHECK   DW_AT_upper_bound (DW_OP_push_object_address, DW_OP_plus_uconst 0xa8, DW_OP_deref)
+; CHECK   DW_AT_byte_stride (DW_OP_push_object_address, DW_OP_plus_uconst 0xa0, DW_OP_deref, DW_OP_lit4, DW_OP_mul)
+; CHECK: DW_TAG_subrange_type
+; CHECK   DW_AT_lower_bound (DW_OP_push_object_address, DW_OP_plus_uconst 0xb0, DW_OP_deref)
+; CHECK   DW_AT_upper_bound (DW_OP_push_object_address, DW_OP_plus_uconst 0xd8, DW_OP_deref)
+; CHECK   DW_AT_byte_stride (DW_OP_push_object_address, DW_OP_plus_uconst 0xd0, DW_OP_deref, DW_OP_lit4, DW_OP_mul)
+
+; Test case is hand written with the help of below Fortran source program.
+; Generated IR is meaning less and goal of it is just to check the
+; processing of DWARF operator DW_OP_over.
+;------------------------------
+;program main
+;integer, allocatable :: arr(:,:,:)
+;allocate(arr(2:20,3:30,4:40))
+;arr(2,3,4)=99
+;print *, arr
+;end program main
+;------------------------------
+
+; ModuleID = 'over.ll'
+source_filename = "allocated.ll"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @MAIN_() !dbg !5 {
+L.entry:
+  %.Z0655_362 = alloca i32*, align 8
+  %"arr$sd1_379" = alloca [28 x i64], align 8
+  call void @llvm.dbg.declare(metadata i32** %.Z0655_362, metadata !8, metadata !DIExpression()), !dbg !11
+  call void @llvm.dbg.declare(metadata i32** %.Z0655_362, metadata !12, metadata !DIExpression()), !dbg !11
+  call void @llvm.dbg.declare(metadata [28 x i64]* %"arr$sd1_379", metadata !14, metadata !DIExpression()), !dbg !11
+  call void @llvm.dbg.declare(metadata [28 x i64]* %"arr$sd1_379", metadata !19, metadata !DIExpression()), !dbg !11
+  ret void, !dbg !25
+}
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+
+!llvm.module.flags = !{!0, !1}
+!llvm.dbg.cu = !{!2}
+
+!0 = !{i32 2, !"Dwarf Version", i32 4}
+!1 = !{i32 2, !"Debug Info Version", i32 3}
+!2 = distinct !DICompileUnit(language: DW_LANG_Fortran90, file: !3, producer: " F90 Flang 1.5 2017-05-01", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, retainedTypes: !4, globals: !4, imports: !4)
+!3 = !DIFile(filename: "over.f90", directory: "/dir")
+!4 = !{}
+!5 = distinct !DISubprogram(name: "main", scope: !2, file: !3, line: 1, type: !6, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagMainSubprogram, unit: !2)
+!6 = !DISubroutineType(cc: DW_CC_program, types: !7)
+!7 = !{null}
+!8 = distinct !DILocalVariable(scope: !5, file: !3, type: !9, flags: DIFlagArtificial)
+!9 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !10, size: 64, align: 64)
+!10 = !DIBasicType(name: "integer", size: 32, align: 32, encoding: DW_ATE_signed)
+!11 = !DILocation(line: 0, scope: !5)
+!12 = distinct !DILocalVariable(scope: !5, file: !3, type: !13, flags: DIFlagArtificial)
+!13 = !DIBasicType(name: "logical", size: 32, align: 32, encoding: DW_ATE_boolean)
+!14 = distinct !DILocalVariable(name: "descriptor", scope: !5, file: !3, type: !15)
+!15 = !DICompositeType(tag: DW_TAG_array_type, baseType: !16, size: 1792, align: 64, elements: !17)
+!16 = !DIBasicType(name: "integer*8", size: 64, align: 64, encoding: DW_ATE_signed)
+!17 = !{!18}
+!18 = !DISubrange(lowerBound: 1, upperBound: 28)
+!19 = !DILocalVariable(name: "arr", scope: !5, file: !3, type: !20)
+!20 = !DICompositeType(tag: DW_TAG_array_type, baseType: !10, size: 32, align: 32, elements: !21, dataLocation: !8, allocated: !12)
+!21 = !{!22, !23, !24}
+!22 = !DISubrange(lowerBound: !DIExpression(DW_OP_push_object_address, DW_OP_over, DW_OP_constu, 48, DW_OP_mul, DW_OP_plus_uconst, 80, DW_OP_plus, DW_OP_deref), upperBound: !DIExpression(DW_OP_push_object_address, DW_OP_over, DW_OP_constu, 48, DW_OP_mul, DW_OP_plus_uconst, 120, DW_OP_plus, DW_OP_deref), stride: !DIExpression(DW_OP_push_object_address, DW_OP_over, DW_OP_constu, 48, DW_OP_mul, DW_OP_plus_uconst, 112, DW_OP_plus, DW_OP_deref, DW_OP_constu, 4, DW_OP_mul))
+!23 = !DISubrange(lowerBound: !DIExpression(DW_OP_push_object_address, DW_OP_plus_uconst, 128, DW_OP_deref), upperBound: !DIExpression(DW_OP_push_object_address, DW_OP_plus_uconst, 168, DW_OP_deref), stride: !DIExpression(DW_OP_push_object_address, DW_OP_plus_uconst, 160, DW_OP_deref, DW_OP_constu, 4, DW_OP_mul))
+!24 = !DISubrange(lowerBound: !DIExpression(DW_OP_push_object_address, DW_OP_plus_uconst, 176, DW_OP_deref), upperBound: !DIExpression(DW_OP_push_object_address, DW_OP_plus_uconst, 216, DW_OP_deref), stride: !DIExpression(DW_OP_push_object_address, DW_OP_plus_uconst, 208, DW_OP_deref, DW_OP_constu, 4, DW_OP_mul))
+!25 = !DILocation(line: 6, column: 1, scope: !5)