Don't replace Undef with null value for Constants

[ykhatav]

Summary

The following patch - (https://reviews.llvm.org/D117300) introduced null's into the debug information and those nulls are expected to be undef values. The RAUW debug info handlers are for instructions, not constants and the debug information expects the value to be undef and not null. This patch tries to fix this behavior by not replacing undef with null value in Constants for debug info metadata.

[bwyma]

In a similar fashion to how instructions are handled according to Delete an IR-level instruction, when a constant is destroyed and cannot be RAUW'd, updating the debug information uses of the constant to undef seems like the correct approach. LGTM.

[StephenTozer]

Good fix, LGTM.

llvm/test/DebugInfo/X86/undef-type-md.ll

21

Nit, can this attribute be removed?

[ykhatav]

Removed the attribute

[fhahn]

Looks like this was submitted as e83543f8c2ef

@ykhatav it looks like it wasn't closed automatically because the commit message was all one line. Please make sure the commit message is properly structured in the future.

llvm/test/DebugInfo/X86/undef-type-md.ll

 
 ; Function Attrs: convergent mustprogress norecurse
 define linkonce_odr spir_func void @foo() #0 align 2 !dbg !5 {
 entry:
   %0 = alloca %"class.1", align 8
   ret void
 }
 
-attributes #0 = { nofree nosync nounwind readnone speculatable willreturn }
-
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!3, !4}
 !llvm.nondebug.metadata= !{!11}
 
 !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang", isOptimized: true, emissionKind: FullDebug)
 !1 = !DIFile(filename: "test.cpp", directory: "/path/to")
 !2 = !{}
 !3 = !{i32 7, !"Dwarf Version", i32 4}
 !4 = !{i32 2, !"Debug Info Version", i32 3}
 !5 = distinct !DISubprogram(name: "foo<param>", scope: !1, file: !1, line: 27, type: !6, scopeLine: 27, spFlags: DISPFlagDefinition, unit: !0, templateParams: !8)
 !6 = !DISubroutineType(types: !7)
 !7 = !{null}
 !8 = !{!9}
 !9 = !DITemplateValueParameter(name: "S", type: !10, value: %"class.1" addrspace(1)* bitcast ({ { float, i32, i8 } } addrspace(1)* @extern_const to %"class.1" addrspace(1)*))
 !10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
 !11 = !{%"class.1" addrspace(1)* bitcast ({ { float, i32, i8 } } addrspace(1)* @extern_const to %"class.1" addrspace(1)*)}