> On Feb 3, 2016, at 1:58 PM, Zachary Turner <ztur...@google.com> wrote: > > I was thinking of a really trivial function that just returned an int or > something. But then again, I don't really know how to write LLVM IR myself > so I was just going off of what other people told me would be possible. I > could be wrong :)
I’m not saying that it is impossible to find such a function, but keep in mind that even the size of int is baked into the IR. -- adrian > > Maybe not worth worrying about if clang never generates this type of code > anyway, just an idea. > > On Wed, Feb 3, 2016 at 1:35 PM Adrian Prantl <apra...@apple.com > <mailto:apra...@apple.com>> wrote: > For context, here are the relevant LLVM discussions: > http://reviews.llvm.org/D16569 <http://reviews.llvm.org/D16569> (D16569: Emit > line 0 line information for interesting 'orphan’ instructions) > http://reviews.llvm.org/D9887 <http://reviews.llvm.org/D9887> > [DebugInfo][FastISel] Prevent using debug location from previous block for > local values > >> On Feb 3, 2016, at 12:56 PM, Zachary Turner <ztur...@google.com >> <mailto:ztur...@google.com>> wrote: >> >> (Also, if clang is not generating code like this currently, maybe it's not a >> priority, but seems worth mentioning the technique anyway, since it could >> have a lot of use for these types of scenarios) >> >> On Wed, Feb 3, 2016 at 12:54 PM Zachary Turner <ztur...@google.com >> <mailto:ztur...@google.com>> wrote: >> I asked around a little bit, and it seems like you do this by hand-writing >> some LLVM IR (limiting yourself to a subset that is sufficiently platform >> independent) and having clang link that in alongside a regular executable. >> Then call your LLVM IR function from C++ and step over it. Would that work? > > LLVM IR is nowhere near platform independent enough for this to be portable. > Of course having a test for a single target is probably still better than > having no test. I’m not sure if the effort of maintaining textual IR (which > tends to change a lot) in the LLDB testsuite is worth it. Another option (not > any less messy) would be to compile the test to assembler with -S insert a > .loc 0 before assembling the file. > > -- adrian > >> >> You'd probably need to talk to one of the LLVM guys to figure out how to do >> that, but it seems like it should work. >> >> Assuming it does, this technique would also open the door to writing a lot >> of test cases that have historically been very difficult to write (such as >> unwinder tests that need frames to be constructed a specific way, etc). >> >> >> >> On Tue, Feb 2, 2016 at 5:31 PM Jim Ingham <jing...@apple.com >> <mailto:jing...@apple.com>> wrote: >> I don't think Clang does this right now, but Adrian says they are >> considering doing it to solve some problems they have with keeping track of >> nested inlines. >> >> Swift does it, but the compiler makes no guarantees as to when this will >> happen. It isn't controlled by some pragma, builtin or whatever. So I know >> some places where it will happen today, but there's no guarantee it will >> continue to happen in the future. So I'll have to write a test that works >> with the current compiler, and fails if the compiler changes so the relevant >> function no longer has line number 0 code right after the prologue. Yuck! >> >> I don't think it will be any different with clang when/if it starts doing >> this. >> >> Jim >> >> >> > On Feb 2, 2016, at 4:14 PM, Zachary Turner <ztur...@google.com >> > <mailto:ztur...@google.com>> wrote: >> > >> > Shouldn't it be possible to force clang to generate code like this? If so >> > couldn't you write a test for this by stepping over a function call which >> > has this kind of code in it? >> > >> > On Tue, Feb 2, 2016 at 4:11 PM Jim Ingham via lldb-commits >> > <lldb-commits@lists.llvm.org <mailto:lldb-commits@lists.llvm.org>> wrote: >> > Author: jingham >> > Date: Tue Feb 2 18:07:23 2016 >> > New Revision: 259611 >> > >> > URL: http://llvm.org/viewvc/llvm-project?rev=259611&view=rev >> > <http://llvm.org/viewvc/llvm-project?rev=259611&view=rev> >> > Log: >> > The compiler may use "line number 0" to indicate compiler generated goo >> > that it can't >> > track a source for. When we are pushing breakpoints and stepping past >> > function prologues, >> > also push past code from line 0 immediately following the prologue end. >> > >> > <rdar://problem/23730696 <>> >> > >> > Modified: >> > lldb/trunk/include/lldb/Symbol/Function.h >> > lldb/trunk/source/Symbol/Function.cpp >> > >> > Modified: lldb/trunk/include/lldb/Symbol/Function.h >> > URL: >> > http://llvm.org/viewvc/llvm-project/lldb/trunk/include/lldb/Symbol/Function.h?rev=259611&r1=259610&r2=259611&view=diff >> > >> > <http://llvm.org/viewvc/llvm-project/lldb/trunk/include/lldb/Symbol/Function.h?rev=259611&r1=259610&r2=259611&view=diff> >> > ============================================================================== >> > --- lldb/trunk/include/lldb/Symbol/Function.h (original) >> > +++ lldb/trunk/include/lldb/Symbol/Function.h Tue Feb 2 18:07:23 2016 >> > @@ -574,6 +574,14 @@ public: >> > CompilerType >> > GetCompilerType (); >> > >> > + //------------------------------------------------------------------ >> > + /// Get the size of the prologue instructions for this function. The >> > "prologue" >> > + /// instructions include any instructions given line number 0 >> > immediately following >> > + /// the prologue end. >> > + /// >> > + /// @return >> > + /// The size of the prologue. >> > + //------------------------------------------------------------------ >> > uint32_t >> > GetPrologueByteSize (); >> > >> > >> > Modified: lldb/trunk/source/Symbol/Function.cpp >> > URL: >> > http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Symbol/Function.cpp?rev=259611&r1=259610&r2=259611&view=diff >> > >> > <http://llvm.org/viewvc/llvm-project/lldb/trunk/source/Symbol/Function.cpp?rev=259611&r1=259610&r2=259611&view=diff> >> > ============================================================================== >> > --- lldb/trunk/source/Symbol/Function.cpp (original) >> > +++ lldb/trunk/source/Symbol/Function.cpp Tue Feb 2 18:07:23 2016 >> > @@ -570,6 +570,8 @@ Function::GetPrologueByteSize () >> > { >> > m_flags.Set(flagsCalculatedPrologueSize); >> > LineTable* line_table = m_comp_unit->GetLineTable (); >> > + uint32_t prologue_end_line_idx = 0; >> > + >> > if (line_table) >> > { >> > LineEntry first_line_entry; >> > @@ -578,9 +580,12 @@ Function::GetPrologueByteSize () >> > { >> > // Make sure the first line entry isn't already the end >> > of the prologue >> > addr_t prologue_end_file_addr = LLDB_INVALID_ADDRESS; >> > + addr_t line_zero_end_file_addr = LLDB_INVALID_ADDRESS; >> > + >> > if (first_line_entry.is_prologue_end) >> > { >> > prologue_end_file_addr = >> > first_line_entry.range.GetBaseAddress().GetFileAddress(); >> > + prologue_end_line_idx = first_line_entry_idx; >> > } >> > else >> > { >> > @@ -595,6 +600,7 @@ Function::GetPrologueByteSize () >> > if (line_entry.is_prologue_end) >> > { >> > prologue_end_file_addr = >> > line_entry.range.GetBaseAddress().GetFileAddress(); >> > + prologue_end_line_idx = idx; >> > break; >> > } >> > } >> > @@ -607,7 +613,7 @@ Function::GetPrologueByteSize () >> > { >> > // Check the first few instructions and look for one >> > that has >> > // a line number that's different than the first >> > entry. >> > - const uint32_t last_line_entry_idx = >> > first_line_entry_idx + 6; >> > + uint32_t last_line_entry_idx = first_line_entry_idx + >> > 6; >> > for (uint32_t idx = first_line_entry_idx + 1; idx < >> > last_line_entry_idx; ++idx) >> > { >> > LineEntry line_entry; >> > @@ -616,6 +622,7 @@ Function::GetPrologueByteSize () >> > if (line_entry.line != first_line_entry.line) >> > { >> > prologue_end_file_addr = >> > line_entry.range.GetBaseAddress().GetFileAddress(); >> > + prologue_end_line_idx = idx; >> > break; >> > } >> > } >> > @@ -624,10 +631,37 @@ Function::GetPrologueByteSize () >> > if (prologue_end_file_addr == LLDB_INVALID_ADDRESS) >> > { >> > prologue_end_file_addr = >> > first_line_entry.range.GetBaseAddress().GetFileAddress() + >> > first_line_entry.range.GetByteSize(); >> > + prologue_end_line_idx = first_line_entry_idx; >> > } >> > } >> > + >> > const addr_t func_start_file_addr = >> > m_range.GetBaseAddress().GetFileAddress(); >> > const addr_t func_end_file_addr = func_start_file_addr + >> > m_range.GetByteSize(); >> > + >> > + // Now calculate the offset to pass the subsequent line 0 >> > entries. >> > + uint32_t first_non_zero_line = prologue_end_line_idx; >> > + while (1) >> > + { >> > + LineEntry line_entry; >> > + if >> > (line_table->GetLineEntryAtIndex(first_non_zero_line, line_entry)) >> > + { >> > + if (line_entry.line != 0) >> > + break; >> > + } >> > + if >> > (line_entry.range.GetBaseAddress().GetFileAddress() >= func_end_file_addr) >> > + break; >> > + >> > + first_non_zero_line++; >> > + } >> > + >> > + if (first_non_zero_line > prologue_end_line_idx) >> > + { >> > + LineEntry first_non_zero_entry; >> > + if >> > (line_table->GetLineEntryAtIndex(first_non_zero_line, >> > first_non_zero_entry)) >> > + { >> > + line_zero_end_file_addr = >> > first_non_zero_entry.range.GetBaseAddress().GetFileAddress(); >> > + } >> > + } >> > >> > // Verify that this prologue end file address in the >> > function's >> > // address range just to be sure >> > @@ -635,10 +669,16 @@ Function::GetPrologueByteSize () >> > { >> > m_prologue_byte_size = prologue_end_file_addr - >> > func_start_file_addr; >> > } >> > + >> > + if (prologue_end_file_addr < line_zero_end_file_addr && >> > line_zero_end_file_addr < func_end_file_addr) >> > + { >> > + m_prologue_byte_size += line_zero_end_file_addr - >> > prologue_end_file_addr; >> > + } >> > } >> > } >> > } >> > - return m_prologue_byte_size; >> > + >> > + return m_prologue_byte_size; >> > } >> > >> > lldb::LanguageType >> > >> > >> > _______________________________________________ >> > lldb-commits mailing list >> > lldb-commits@lists.llvm.org <mailto:lldb-commits@lists.llvm.org> >> > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits >> > <http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits> >>
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