Temporary fix for D85085 debug_loc bug with basic block sections.

Until then, this one line fix removes the assert fail with basic block sections
with debug info. Bug tracking this: llvm#47549
This fix does not generate loc list or DW_AT_const_value if the argument is
mentioned in a different section than the start of the function.

Temporarily fixes bugzilla : https://bugs.llvm.org/show_bug.cgi?id=47549

Differential Revision: https://reviews.llvm.org/D87787

llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp

@@ -220,10 +220,16 @@ void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
     // doing that violates the ranges that are calculated in the history map.
     // However, we currently do not emit debug values for constant arguments
     // directly at the start of the function, so this code is still useful.
+    // FIXME: If the first mention of an argument is in a unique section basic
+    // block, we cannot always assign the CurrentFnBeginLabel as it lies in a
+    // different section.  Temporarily, we disable generating loc list
+    // information or DW_AT_const_value when the block is in a different
+    // section.
     const DILocalVariable *DIVar =
         Entries.front().getInstr()->getDebugVariable();
     if (DIVar->isParameter() &&
-        getDISubprogram(DIVar->getScope())->describes(&MF->getFunction())) {
+        getDISubprogram(DIVar->getScope())->describes(&MF->getFunction()) &&
+        Entries.front().getInstr()->getParent()->sameSection(&MF->front())) {
       if (!IsDescribedByReg(Entries.front().getInstr()))
         LabelsBeforeInsn[Entries.front().getInstr()] = Asm->getFunctionBegin();
       if (Entries.front().getInstr()->getDebugExpression()->isFragment()) {

llvm/test/DebugInfo/X86/basic-block-sections-debug-loc.ll

@@ -0,0 +1,87 @@
+;; The dbg value for buflen in the non-entry basic block spans the entire
+;; function and is emitted as DW_AT_const_value.  Even with basic block
+;; sections, this can be done as the entire function is represented as ranges.
+;; FIXME:  Basic block sections should have the same behavior as the default.
+
+; RUN: llc %s --dwarf-version=4 --basic-block-sections=none -filetype=obj -o %t
+; RUN: llvm-dwarfdump %t | FileCheck %s
+; RUN: llc %s --dwarf-version=4 --basic-block-sections=all -filetype=obj -o %t
+; RUN: llvm-dwarfdump %t | FileCheck --check-prefix=MISSING %s
+
+; CHECK:      DW_AT_const_value (157)
+; CHECK-NEXT: DW_AT_name ("buflen")
+; MISSING-NOT:    DW_AT_const_value (157)
+
+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-grtev4-linux-gnu"
+
+define dso_local void @_ZL4ncatPcjz(i8* %0, i32 %1, ...) unnamed_addr  align 32 !dbg !22 {
+.critedge3:
+  call void @llvm.dbg.value(metadata i32 157, metadata !27, metadata !DIExpression()), !dbg !46
+  call void @llvm.va_start(i8* nonnull undef), !dbg !47
+  br label %2
+
+2:                                                ; preds = %2, %.critedge3
+  br label %2
+}
+
+; Function Attrs: nounwind
+declare void @llvm.va_start(i8*) #1
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #2
+
+attributes #1 = { nounwind }
+attributes #2 = { nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!20, !21}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, retainedTypes: !2)
+!1 = !DIFile(filename: "bug.cpp", directory: "/proc/self/cwd")
+!2 = !{!3, !6, !9, !10, !11, !13, !16, !17, !15}
+!3 = !DIDerivedType(tag: DW_TAG_typedef, name: "int32_t", file: !4, line: 38, baseType: !5)
+!4 = !DIFile(filename: "stdint.h", directory: "/proc/self/cwd")
+!5 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!6 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !7, size: 64)
+!7 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !8)
+!8 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_unsigned_char)
+!9 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !8, size: 64)
+!10 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+!11 = !DIDerivedType(tag: DW_TAG_typedef, name: "uint32_t", file: !4, line: 51, baseType: !12)
+!12 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
+!13 = !DIDerivedType(tag: DW_TAG_typedef, name: "UChar", file: !14, line: 372, baseType: !15)
+!14 = !DIFile(filename: "umachine.h", directory: "/proc/self/cwd")
+!15 = !DIBasicType(name: "char16_t", size: 16, encoding: DW_ATE_UTF)
+!16 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !3, size: 64)
+!17 = !DIDerivedType(tag: DW_TAG_typedef, name: "UBool", file: !14, line: 261, baseType: !18)
+!18 = !DIDerivedType(tag: DW_TAG_typedef, name: "int8_t", file: !4, line: 36, baseType: !19)
+!19 = !DIBasicType(name: "signed char", size: 8, encoding: DW_ATE_signed_char)
+!20 = !{i32 2, !"Debug Info Version", i32 3}
+!21 = !{i32 7, !"PIC Level", i32 2}
+!22 = distinct !DISubprogram(name: "ncat", linkageName: "_ZL4ncatPcjz", scope: !1, file: !1, line: 37, type: !23, scopeLine: 37, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !25)
+!23 = !DISubroutineType(types: !24)
+!24 = !{!3, !9, !11, null}
+!25 = !{!26, !27, !28, !41, !42, !43, !44}
+!26 = !DILocalVariable(name: "buffer", arg: 1, scope: !22, file: !1, line: 37, type: !9)
+!27 = !DILocalVariable(name: "buflen", arg: 2, scope: !22, file: !1, line: 37, type: !11)
+!28 = !DILocalVariable(name: "args", scope: !22, file: !1, line: 38, type: !29)
+!29 = !DIDerivedType(tag: DW_TAG_typedef, name: "va_list", file: !30, line: 14, baseType: !31)
+!30 = !DIFile(filename: "stdarg.h", directory: "/proc/self/cwd")
+!31 = !DIDerivedType(tag: DW_TAG_typedef, name: "__builtin_va_list", file: !1, line: 38, baseType: !32)
+!32 = !DICompositeType(tag: DW_TAG_array_type, baseType: !33, size: 192, elements: !39)
+!33 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "__va_list_tag", file: !1, line: 38, size: 192, flags: DIFlagTypePassByValue, elements: !34, identifier: "_ZTS13__va_list_tag")
+!34 = !{!35, !36, !37, !38}
+!35 = !DIDerivedType(tag: DW_TAG_member, name: "gp_offset", scope: !33, file: !1, line: 38, baseType: !12, size: 32)
+!36 = !DIDerivedType(tag: DW_TAG_member, name: "fp_offset", scope: !33, file: !1, line: 38, baseType: !12, size: 32, offset: 32)
+!37 = !DIDerivedType(tag: DW_TAG_member, name: "overflow_arg_area", scope: !33, file: !1, line: 38, baseType: !10, size: 64, offset: 64)
+!38 = !DIDerivedType(tag: DW_TAG_member, name: "reg_save_area", scope: !33, file: !1, line: 38, baseType: !10, size: 64, offset: 128)
+!39 = !{!40}
+!40 = !DISubrange(count: 1)
+!41 = !DILocalVariable(name: "str", scope: !22, file: !1, line: 39, type: !9)
+!42 = !DILocalVariable(name: "p", scope: !22, file: !1, line: 40, type: !9)
+!43 = !DILocalVariable(name: "e", scope: !22, file: !1, line: 41, type: !6)
+!44 = !DILocalVariable(name: "c", scope: !45, file: !1, line: 49, type: !8)
+!45 = distinct !DILexicalBlock(scope: !22, file: !1, line: 48, column: 45)
+!46 = !DILocation(line: 0, scope: !22)
+!47 = !DILocation(line: 47, column: 3, scope: !22)