[llvm-dev] PPC64 Disassembler

[Nemanja Ivanovic via llvm-dev]

The `isBranch` flag is already set on the branch instructions. Furthermore,
we do use the `isBranch()` query in a few places in the PPC back end, so
this does work. Perhaps there's something specific about the lldb usage? Is
it somehow possible that the `isBranch()` query is called on the wrong
instruction?
Would you be able to provide a test case that reproduces the issue?

On Thu, Nov 30, 2017 at 2:30 AM, Sean Fertile via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hello Leonardo,
>
> What is the opcode of the MCInstrDesc?
>
> Sean
>
> On Wed, Nov 29, 2017 at 1:48 PM, Leonardo Bianconi via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > Hi all,
> >
> >
> >
> > I’m working on lldb to make it available to ppc64le, but the “step over”
> >
> > is not working for some cases.
> >
> >
> >
> > When debugging, I can see that the disassembler analyze some instructions
> >
> > forward, looking for a branch instruction
> >
> > (llvm/tools/lldb/source/Plugins/Disassembler/llvm/
> DisassemblerLLVMC.cpp:87
> >
> > – “const bool can_branch = mc_disasm_ptr->CanBranch(inst);”), while
> >
> > trying to set the next breakpoint.
> >
> >
> >
> > On this case, the instruction is the “bne     cr7,0x2000092c”, which is a
> > branch,
> >
> > but at llvm/lib/MC/MCInstrDesc.cpp:35 –
> >
> > “if (isBranch() || isCall() || isReturn() || isIndirectBranch())” it
> returns
> > false,
> >
> > making lldb do not set the correct breakpoint, so the execution does not
> > stop
> >
> > at next line, which should be the “step over” behavior.
> >
> >
> >
> > The variable “Flags” for the disassembled instruction does not have the
> > branch
> >
> > flag.
> >
> >
> >
> > I have tried to change the file “/lib/Target/PowerPC/PPCInstrInfo.td”,
> > adding
> >
> > “isBranch = 1” for the instruction "bc 4, $bi, $dst", but had not effect.
> >
> >
> >
> > Comparing with x86_64, building the same cpp file, the instruction
> >
> > “jne    0x4005eb” has the branch flag, which identifies it as a branch
> > instruction.
> >
> >
> >
> > Where is the definition that an instruction is a branch? Is it a bug?
> >
> >
> >
> > Thanks!
> >
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
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