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<big>I've finally figured out where a function </big>declaration is
lazily emitted. It is done in the
CodeGenModule::GetOrCreateLLVMFunction() function, which is in
turned called by EmitCall functions. I wrote a function which is
similar to the CGDebugInfo::EmitFunctionStart() function and hooked
it into the GetOrCreateLLVMFunction function. It seems to work,
since it passed all LLVM & Clang regression tests except two.<br>
<br>
I'm now having two other questions.<br>
<br>
(1) How to add a Clang command line option to control the call to my
function? The hook-up point in my code is as follows:<br>
<br>
<font face="Courier New, Courier, monospace">llvm::Constant *<br>
CodeGenModule::GetOrCreateLLVMFunction(StringRef MangledName,<br>
llvm::Type *Ty,<br>
GlobalDecl D, bool
ForVTable,<br>
llvm::AttributeSet
ExtraAttrs) {<br>
...<br>
llvm::Function *F = llvm::Function::Create(FTy,<br>
llvm::Function::ExternalLinkage,<br>
MangledName,
&getModule());<br>
...<br>
if (ExtraAttrs.hasAttributes(llvm::AttributeSet::FunctionIndex))
{<br>
llvm::AttrBuilder B(ExtraAttrs,
llvm::AttributeSet::FunctionIndex);<br>
F->addAttributes(llvm::AttributeSet::FunctionIndex,<br>
llvm::AttributeSet::get(VMContext,<br>
llvm::AttributeSet::FunctionIndex,<br>
B));<br>
}<br>
<br>
// Emit subprogram debug descriptor for this new declaration<br>
// if "-gg" is given like clang -gg, then call this function<br>
EmitFunctionDeclaration(D, F); </font><font face="Courier
New, Courier, monospace"><font face="Courier New, Courier,
monospace">-- hook up line</font><br>
<br>
// This is the first use or definition of a mangled name. If
there is a<br>
// deferred decl with this name, remember that we need to emit
it at the end<br>
// of the file.<br>
llvm::StringMap<GlobalDecl>::iterator DDI =
DeferredDecls.find(MangledName);<br>
...<br>
}<br>
</font><br>
It seems to be very complicated to do this in Clang. I've spent
hours and still couldn't solve it.<br>
<br>
(2) I've run LLVM&Clang regression tests on my code and there
are two failures. One of them is debug-info-class.cpp (the other is
debug-info-template-quals.cpp), and the failure message is:<br>
<br>
<font face="Courier New, Courier, monospace">llvm-3.3.src/tools/clang/test/CodeGenCXX/debug-info-class.cpp:45:11:
error: expected string not found in input<br>
// CHECK: DW_TAG_class_type ] [B]<br>
^<br>
<stdin>:230:75: note: scanning from here<br>
!49 = metadata !{i32 786445, metadata !1, metadata !46, metadata
!"HdrSize", i32 17, i64 0, i64 0, i64 0, i32 4096, metadata !50,
i32 52} ; [ DW_TAG_member ] [HdrSize] [line 17, size 0, align 0,
offset 0] [static] [from ]<br>
^<br>
<stdin>:231:109: note: possible intended match here<br>
!50 = metadata !{i32 786470, null, null, metadata !"", i32 0, i64
0, i64 0, i64 0, i32 0, metadata !23} ; [ DW_TAG_const_type ]
[line 0, size 0, align 0, offset 0] [from int]<br>
^<br>
--</font><br>
<br>
However, the generated bitcode assembly does have <font
face="Courier New, Courier, monospace">DW_TAG_class_type ] [B]</font>.
The related entry is:<br>
<br>
<font face="Courier New, Courier, monospace">!31 = metadata !{i32
786434, metadata !1, null, metadata !"B", i32 11, i64 64, i64 64,
i32 0, i32 0, null, metadata !32, i32 0, metadata !31, null} ; [
DW_TAG_class_type ] [B] [line 11, size 64, align 64, offset 0]
[from ]<br>
</font><br>
I've attached the entire code to the letter. I'm wondering what is
going, and how can I solve this?<br>
<br>
Thanks very much<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 11/12/2013 03:06 PM, Eric
Christopher wrote:<br>
</div>
<blockquote
cite="mid:CALehDX6XWPK5OvJLDy+6tjYCRANduuKQM97dtJQ_LMnVQiU7VA@mail.gmail.com"
type="cite">
<pre wrap="">On Mon, Nov 11, 2013 at 4:13 PM, Lewis Burns <a class="moz-txt-link-rfc2396E" href="mailto:lewisurn@gmail.com"><lewisurn@gmail.com></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">No, I don't care about those functions that aren't called.
Okay, I walked through the EmitCall family of functions of CodeGenFunction,
but didn't notice much. I guess that I'll have to trace them through more
carefully to see when it is done.
My thought is to copy the debug info metadata emission logic used during
generating the function prolog to function declarations. Do you think if it
works?
</pre>
</blockquote>
<pre wrap="">
Easiest is looking at getOrCreateFunctionType. You can probably hook
into EmitCall if you want to emit a debug info declaration for the
function.
-eric
</pre>
<blockquote type="cite">
<pre wrap="">Thanks,
On 11/12/2013 07:49 AM, David Blaikie wrote:
Do you care about generating debug info for declarations of functions that
aren't even called? If so, then the approach you're taking will be
insufficient (since we won't even emit an IR declaration for such a
function)
If not, then you might want to take a look at where the IR for the call is
constructed (I don't know where this is, but you seem to be gaining some
proficiency tracing through Clang/LLVM internals that will serve you well
here) and then see how the target of the call is built and passed in to
that.
On Mon, Nov 11, 2013 at 3:44 PM, Lewis Burns <a class="moz-txt-link-rfc2396E" href="mailto:lewisurn@gmail.com"><lewisurn@gmail.com></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">
I ran Clang in a debugger and traced how debug info metadata was emitted.
It's a part of code generation of functions.
I have a question about when the declaration of an extern function is
emitted. For example, I have very simple code:
extern int convert(unsigned u);
void foo() {
int x = convert(0);
}
The corresponding LLVM code is:
...
; Function Attrs: nounwind uwtable
define void @foo() #0 {
entry:
%x = alloca i32, align 4
call void @llvm.dbg.declare(metadata !{i32* %x}, metadata !8), !dbg !10
%call = call i32 @convert(i32 0), !dbg !10
store i32 %call, i32* %x, align 4, !dbg !10
ret void, !dbg !11
}
...
declare i32 @convert(i32) #2 // when this line is emitted
My question is where the "declare i32 @convert(i32) #2" line is emitted. I
tried many breakpoints in EmitXXX family of functions in CodeGenModule and
noticed that this piece of code
// Ignore declarations, they will be emitted on their first use.
if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(Global)) {
// Forward declarations are emitted lazily on first use.
if (!FD->doesThisDeclarationHaveABody()) {
if (!FD->doesDeclarationForceExternallyVisibleDefinition())
return;
causes the postpone of emission of the convert function declaration, but I
couldn't figure out where and when the declaration is emitted. I set a
breakpoint in the CodeGenModule::EmitDeferred() function, but nothing was
done in that function.
Any help is really appreciated.
On 11/09/2013 04:14 PM, David Blaikie wrote:
For those following this thread a critical detail would be that you want
debug info metadata.
There's no simple flag for this as we don't attach the function debug info
metadata to every declaration, just to definitions (there's no filtering
step)
But why do you want this anyway? If you're performing
optimizations/transformations based on debug info metadata, that's not
really the desired approach. Debug info is not meant to affect code
generation.
On Nov 9, 2013 7:59 AM, "Lewis Burns" <a class="moz-txt-link-rfc2396E" href="mailto:lewisurn@gmail.com"><lewisurn@gmail.com></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">
Hi,
I haven't worked on Clang before and have a simple question (supposedly)
for those who are familiar with metadata and LLVM bitcode generation. Assume
that I have a function which is declared as extern as the following:
extern int convert(unsigned u);
I want to have Clang generate metadata nodes for it by adding a metadata
node of subprogram into the list of subprograms defined in the current
compilation unit. The subprogram metadata node and its associated nodes
should have the info of the type signature. For example, I get the following
set of metadata nodes for function
int convert(unsigned u) {return 0;}
!3 = metadata !{metadata !4, metadata !10, metadata !33}
!4 = metadata !{i32 786478, metadata !1, metadata !5, metadata
!"convert", metadata !"convert", metadata !"", i32 23, metadata !6, i1
false, i1 true, i32 0, i32 0, null, i32 256, i1 false, i32 (i32)* @convert,
null, null, metadata !2, i32 23} ; [ DW_TAG_subprogram ] [line 23] [def]
[convert]
!7 = metadata !{metadata !8, metadata !9}
!8 = metadata !{i32 786468, null, null, metadata !"int", i32 0, i64 32,
i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ] [int] [line 0, size 32,
align 32, offset 0, enc DW_ATE_signed]
!9 = metadata !{i32 786468, null, null, metadata !"unsigned int", i32 0,
i64 32, i64 32, i64 0, i32 0, i32 7} ; [ DW_TAG_base_type ] [unsigned int]
[line 0, size 32, align 32, offset 0, enc DW_ATE_unsigned]
which allows me to extract the source-level type signature for the
function by using LLVM debug info APIs. I'd like to get the source-level
type signature of the extern declared function, but Clang does not produce
metadata for it.
By looking at the Clang AST for the extern declared function
|-FunctionDecl 0x70598c0 <line:23:1, col:30> convert 'int (unsigned int)'
extern
| |-ParmVarDecl 0x7059800 <col:20, col:29> u 'unsigned int'
I know that Clang has the information I need, and I just need to turn off
or remove the filter that ignores functions whose bodies are not available
during metadata node or/and code generation. Are there simple switches that
do this? If not, can anyone please explain how to do it by pointing me to
the right code snippets?
Thanks very much,
--
Lewis
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</pre>
</blockquote>
<pre wrap="">
--
Lewis
</pre>
</blockquote>
<pre wrap="">
--
Lewis
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</pre>
</blockquote>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Lewis</pre>
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