code_* cleanup, and strip IR metadata from code_llvm output

[ihnorton]

(replaces #10741 ... because github)

The first commit cleans up the code_native and code_llvm pathways a little bit by removing an intermediate function and calling the one we want directly from Julia code.

The second commit changes the behavior of code_llvm to strip all metadata before printing the IR. This reduces the work needed to run code_llvm output with lli for debugging purposes. I also added a code_llvm_raw version with the current behavior. If people don't think stripped should be the default I'll switch it around.

Should now compile against gcc 4.6.

before:

; Function Attrs: uwtable
define void @julia_bf_112785(i32, i64) #0 {
top:
  call void @llvm.dbg.value(metadata i32 %0, i64 0, metadata !11, metadata !17)
  call void @llvm.dbg.value(metadata i64 %1, i64 0, metadata !18, metadata !17)
  %sext = shl i32 %0, 24, !dbg !19
  %2 = ashr exact i32 %sext, 24, !dbg !19
  %3 = icmp eq i32 %2, %0, !dbg !19
  br i1 %3, label %pass, label %fail, !dbg !19
...

after:

; Function Attrs: uwtable
define void @julia_bf_112785(i32, i64) #-1 {
top:
  %sext = shl i32 %0, 24
  %2 = ashr exact i32 %sext, 24
  %3 = icmp eq i32 %2, %0
  br i1 %3, label %pass, label %fail

[ihnorton]

Now removes these lines as well:

  call void @llvm.dbg.value(metadata i32 %0, i64 0, metadata !0, metadata !13)
  call void @llvm.dbg.value(metadata i64 %1, i64 0, metadata !14, metadata !13)

Also added a helper function jl_function_ptr_by_llvm_name. The purpose is to allow copying a mangled julia_... name from a code_llvm dump, then call jl_function_ptr_by_llvm_name to get the corresponding Function*, then call the refactored dumper functions directly (without needing to figure out the corresponding Julia signature).

It would be nice to have a way to go all the way back to the original Julia method signature from one of these mangled names, but I don't think we store that mapping anywhere. FuncInfo has the Function* and the name, but to get back to the original type signature would (I think) require iterating over all methods and looking at the attached functionObject.

[Keno]

Thanks @ihnorton. I can't quite tell if the windows failure is related or not, but otherwise, LGTM. This is a much needed cleanup.

[tkelman]

Definitely related. The added include from codegen.cpp:11 either needs a flag that is getting set in the linux build but not the windows build, or the headers themselves go down different codepaths which are broken for windows

[ihnorton]

Thanks. Should be fixed now, will let appveyor run through. I am on windows, but using llvm-3.6 and forgot to remove a line that is incompatible with 3.3.

[ihnorton]

Also added this notice to the output of code_llvm:

; NOTE: Instruction metadata and dbg.* calls have been removed.
;       Use Base.code_llvm_raw for full IR.

[StefanKarpinski]

I don't think the notice is necessary – it should suffice to put this in the documentation of code_llvm.

[simonster]

This certainly shouldn't hold up this PR, but is it possible to turn the debug metadata into line numbers? Right now we get them in code_typed and code_native, but not code_llvm.

[ihnorton]

Good point -- that would be a much more useful thing to do with the data before throwing it away. I'll have to get a bit more familiar with how the debug locations work, but will see what I can do (there is enough information in the system to eventually make the DWARF annotations, so it must be possible).

[simonster]

@ihnorton Is it possible to show just the TBAA metadata? I'm finding that I miss it. I know I can get it with code_llvm_raw, but that's a bit less convenient since there's no @code_llvm_raw macro. Alternatively I could just add that macro.

[ihnorton]

@simonster this will preserve TBAA MDNodes:

diff --git a/src/codegen.cpp b/src/codegen.cpp
index 4575080..b2a8f34 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -1016,6 +1016,8 @@ const jl_value_t *jl_dump_function_ir(void *f, bool strip_ir_metadata)

                 // iterate over all metadata kinds and set to NULL to remove
                 for (; md_iter != MDForInst.end(); ++md_iter) {
+                    if ((*md_iter).first == LLVMContext::MD_tbaa)
+                        continue;
                     inst->setMetadata((*md_iter).first, NULL);
                 }
             }