[lldb-dev] IRInterpreter strange behavior

[Zachary Turner]

I'm trying to diagnose a problem with the IRInterpreter, but this is all
very foreign to me so I think I should ask here.

Before I go into the details though, a simple question which I don't want
to get lost in the shuffle:  Why doesn't LLDB use LLI instead of creating
its own interpreter?

Anyway, on to the problem.  First of all, this is only on Windows.  This
all just works on Linux and presumably Mac, although I don't have a Mac to
test.  The scenario is this: I run the following two commands:

(lldb) expr const unsigned int $foo = 5
(lldb) expr &$foo

And this results in an error.  Printing the value of $foo works fine, it
just can't get the address.

I turn on logging and I see this:

Module as passed in to IRInterpreter::Interpret:
"; ModuleID = '$__lldb_module'
target datalayout = "e-m:w-p:32:32-i64:64-f80:32-n8:16:32-S32"
target triple = "i686-pc-windows-msvc"

*@"\01?$S1@?0??$__lldb_expr@@YAXPAX at Z@4IA" = internal global i32 0*

; Function Attrs: nounwind
define void @"\01?$__lldb_expr@@YAXPAX at Z"(i8* %"$__lldb_arg") #0 {
  %1 = getelementptr i8* %"$__lldb_arg", i32 8
  %2 = bitcast i8* %1 to i32**
  %3 = getelementptr i8* %"$__lldb_arg", i32 0
  %4 = bitcast i8* %3 to i32***
  %5 = load i32*** %4
  %6 = alloca i8*, align 4, !clang.decl.ptr !8
  store i8* %"$__lldb_arg", i8** %6, align 4
*  %7 = load i32* @"\01?$S1@?0??$__lldb_expr@@YAXPAX at Z@4IA"*
  %8 = and i32 %7, 1
  %9 = icmp ne i32 %8, 0
  br i1 %9, label %13, label %10

; <label>:10                                      ; preds = %0
  %11 = or i32 %7, 1
  store i32 %11, i32* @"\01?$S1@?0??$__lldb_expr@@YAXPAX at Z@4IA"
  %12 = load i32** %2, align 4
  store i32* %12, i32** %5, align 4
  br label %13

; <label>:13                                      ; preds = %10, %0
  ret void
}

attributes #0 = { nounwind "less-precise-fpmad"="false"
"no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"
"no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-realign-stack"
"stack-protector-buffer-size"="0" "unsafe-fp-math"="false"
"use-soft-float"="false" }

!clang.global.decl.ptrs = !{!0, !1, !2, !0, !0}
!llvm.module.flags = !{!3, !4, !5, !6}
!llvm.ident = !{!7}

!0 = metadata !{null, i64 7787680}
!1 = metadata !{null, i64 7787504}
!2 = metadata !{void (i8*)* @"\01?$__lldb_expr@@YAXPAX at Z", i64 7787328}
!3 = metadata !{i32 1, metadata !"Objective-C Version", i32 2}
!4 = metadata !{i32 1, metadata !"Objective-C Image Info Version", i32 0}
!5 = metadata !{i32 1, metadata !"Objective-C Image Info Section", metadata
!"__DATA, __objc_imageinfo, regular, no_dead_strip"}
!6 = metadata !{i32 4, metadata !"Objective-C Garbage Collection", i32 0}
!7 = metadata !{metadata !"clang version 3.5.0 "}
!8 = metadata !{i64 7787200}
"
IRMemoryMap::WriteMemory (0x81ffc, 0x124db54, 0x4) went to [0x2000..0x82000)
Made an allocation for argument i8* %"$__lldb_arg"
  Data region    : 1000
  Ref region     : 81ffc
Interpreting %1 = getelementptr i8* %"$__lldb_arg", i32 8
IRMemoryMap::WriteMemory (0x81ff8, 0x702b00, 0x4) went to [0x2000..0x82000)
Interpreted a GetElementPtrInst
  P       : i8* %"$__lldb_arg" 0x81ffc
  Poffset : %1 = getelementptr i8* %"$__lldb_arg", i32 8 0x81ff8
Interpreting %2 = bitcast i8* %1 to i32**
IRMemoryMap::WriteMemory (0x81ff4, 0x702b00, 0x4) went to [0x2000..0x82000)
Interpreting %3 = getelementptr i8* %"$__lldb_arg", i32 0
IRMemoryMap::WriteMemory (0x81ff0, 0x702b00, 0x4) went to [0x2000..0x82000)
Interpreted a GetElementPtrInst
  P       : i8* %"$__lldb_arg" 0x81ffc
  Poffset : %3 = getelementptr i8* %"$__lldb_arg", i32 0 0x81ff0
Interpreting %4 = bitcast i8* %3 to i32***
IRMemoryMap::WriteMemory (0x81fec, 0x702b00, 0x4) went to [0x2000..0x82000)
Interpreting %5 = load i32*** %4
IRMemoryMap::ReadMemory (0x81fec, 0x702b00, 0x4) came from [0x2000..0x82000)
IRMemoryMap::ReadMemory (0x1000, 0x702b00, 0x4) came from [0x1000..0x1010)
IRMemoryMap::WriteMemory (0x81fe8, 0x702b00, 0x4) went to [0x2000..0x82000)
Interpreted a LoadInst
  P : 0x81fec
  R : 0x1000
  D : 0x81fe8
Interpreting %6 = alloca i8*, align 4, !clang.decl.ptr !8
IRMemoryMap::WriteMemory (0x81fe0, 0x124dc00, 0x4) went to [0x2000..0x82000)
Interpreted an AllocaInst
  R : 0x81fe4
  P : 0x81fe0
Interpreting store i8* %"$__lldb_arg", i8** %6, align 4
IRMemoryMap::ReadMemory (0x81fe0, 0x702b00, 0x4) came from [0x2000..0x82000)
IRMemoryMap::ReadMemory (0x81ffc, 0x702b00, 0x4) came from [0x2000..0x82000)
IRMemoryMap::WriteMemory (0x81fe4, 0x702b00, 0x4) went to [0x2000..0x82000)
Interpreted a StoreInst
  D : 0x81ffc
  P : 0x81fe0
  R : 0x81fe4
*Interpreting %7 = load i32* @"\01?$S1@?0??$__lldb_expr@@YAXPAX at Z@4IA"*
*LoadInst's pointer doesn't resolve to anything*

I've bolded a few of the relevant lines.  I'm not really sure what's going
on here, or even how to diagnose it.  Can anyone offer some advice?

Thanks
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