Temporary fix for debug loc list bug with basic block sections

[tmsriram]

Summary

The proper fix for this is being worked out in D85085.

Until then, this one line fix removes the assert fail with basic block sections with debug info. Bug tracking this: #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

[dblaikie]

Could you include the source and any command lines (clang, what optimization level, etc) was used to generate the test IR? It can make the test a bit easier to read at a glance and help if the test needs to be regenerated for some reason.

[tmsriram]

In D87787#2278384, @dblaikie wrote:

Could you include the source and any command lines (clang, what optimization level, etc) was used to generate the test IR? It can make the test a bit easier to read at a glance and help if the test needs to be regenerated for some reason.

The test IR was reduced using a reduce tool so we don't have the source unfortunately. We tried hard to generate C programs that would show this failure but with no avail.

[dblaikie]

sounds good - thanks!

[snehasish]

ping @tmsriram
Lets push this if it's good to go?

llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp

for (const auto &I : DbgValues) {
     // so arguments are visible when breaking at function entry.
     //
     // We do not change the label for values that are described by registers,
     // as that could place them above their defining instructions. We should
     // ideally not change the labels for constant debug values either, since
     // 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()) {
         // Mark all non-overlapping initial fragments.
         for (auto I = Entries.begin(); I != Entries.end(); ++I) {
           if (!I->isDbgValue())
             continue;
           const DIExpression *Fragment = I->getInstr()->getDebugExpression();

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

+;; 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)