[LLDB] Added support for PHI nodes to IR interpreter

[cameron314]

Summary

This allows expressions such as 'i == 1 || i == 2` to be executed using the IR interpreter.

[zturner]

I'll let Sean comment on the content of the patch, but please add a test
that runs such an expression and demonstrates the correct output.

[cameron314]

Ah, that's a bit tricky at the moment. The LLVM tip no longer compiles with VS2015 (specifically lib\Support\SourceMgr.cpp), and my Python setup for VS2013 is all wonky.
This will have to wait a bit.

[zturner]

http://lab.llvm.org:8011/builders/lldb-x86-windows-msvc2015

My build bot which uses MSVC 2015 is workign fine. What kind of error are
you seeing?

[cameron314]

Whoops, my fault. I was accidentally using the VS2013 command prompt with the 2015 cmake files. Compiling happily as we speak, test coming up soon after.

[cameron314]

I've added a test for this patch.

[cameron314]

I'd appreciate if someone could take a look at this when they have a moment.

[zturner]

This is going to have to be Sean, but his delay can be unpredictable. Keep
pinging every so often until you get a response

[cameron314]

All right, no worries :-) I didn't want to bother anyone.

[cameron314]

@spyffe, do you have time to look at this sometime this week? It's a very simple patch (the test code took longer to write than the patch itself). Thanks!

[spyffe]

Ah… you know me too well.
Looking at this now.

[spyffe]

This patch is fine. I especially appreciate the time you took making the IRInterpreter properly testable. I will use this myself.

source/Commands/CommandObjectExpression.cpp

67 ↗

(On Diff #54134)

This is a great feature which I will use in test cases.

source/Expression/IRInterpreter.cpp

1099

Looks all right to me. Thank you!

[cameron314]

Excellent, thank you!

[ovyalov]

Looks like this CL broke CMake build bot - http://lab.llvm.org:8011/builders/lldb-x86_64-ubuntu-14.04-cmake/builds/14634, could you take a look?

source/Expression/IRInterpreter.cpp

 {
 public:
     typedef std::map <const Value*, lldb::addr_t> ValueMap;
 
     ValueMap                                m_values;
     DataLayout                             &m_target_data;
     lldb_private::IRExecutionUnit          &m_execution_unit;
     const BasicBlock                       *m_bb;
+    const BasicBlock                       *m_prev_bb;
     BasicBlock::const_iterator              m_ii;
     BasicBlock::const_iterator              m_ie;
 
     lldb::addr_t                            m_frame_process_address;
     size_t                                  m_frame_size;
     lldb::addr_t                            m_stack_pointer;
 
     lldb::ByteOrder                         m_byte_order;
     size_t                                  m_addr_byte_size;
 
     InterpreterStackFrame (DataLayout &target_data,
                            lldb_private::IRExecutionUnit &execution_unit,
                            lldb::addr_t stack_frame_bottom,
                            lldb::addr_t stack_frame_top) :
         m_target_data (target_data),
-        m_execution_unit (execution_unit)
+        m_execution_unit (execution_unit),
+        m_bb (nullptr),
+        m_prev_bb (nullptr)
     {
         m_byte_order = (target_data.isLittleEndian() ? lldb::eByteOrderLittle : lldb::eByteOrderBig);
         m_addr_byte_size = (target_data.getPointerSize(0));
 
         m_frame_process_address = stack_frame_bottom;
         m_frame_size = stack_frame_top - stack_frame_bottom;
         m_stack_pointer = stack_frame_top;
     }
 
     ~InterpreterStackFrame ()
     {
     }
 
     void Jump (const BasicBlock *bb)
     {
+        m_prev_bb = m_bb;
         m_bb = bb;
         m_ii = m_bb->begin();
         m_ie = m_bb->end();
     }
 
     std::string SummarizeValue (const Value *value)
     {
         lldb_private::StreamString ss;
for (Function::iterator bbi = function.begin(), bbe = function.end();
                     error.SetErrorToGenericError();
                     error.SetErrorString(unsupported_opcode_error);
                     return false;
                 }
             case Instruction::Add:
             case Instruction::Alloca:
             case Instruction::BitCast:
             case Instruction::Br:
+            case Instruction::PHI:
                 break;
             case Instruction::Call:
                 {
                     CallInst *call_inst = dyn_cast<CallInst>(ii);
 
                     if (!call_inst)
                     {
                         error.SetErrorToGenericError();
while (frame.m_ii != frame.m_ie && (++num_insts < 4096))
 
                     if (log)
                     {
                         log->Printf("Interpreted a BrInst with no condition");
                     }
                 }
             }
                 continue;
+            case Instruction::PHI:
+            {
+                const PHINode *phi_inst = dyn_cast<PHINode>(inst);
+
+                if (!phi_inst)
+                {
+                    if (log)
+                        log->Printf("getOpcode() returns PHI, but instruction is not a PHINode");
+                    error.SetErrorToGenericError();
+                    error.SetErrorString(interpreter_internal_error);
+                    return false;
+                }
+                if (!frame.m_prev_bb)
+                {
+                    if (log)
+                        log->Printf("Encountered PHI node without having jumped from another basic block");
+                    error.SetErrorToGenericError();
+                    error.SetErrorString(interpreter_internal_error);
+                    return false;
+                }
+
+                Value* value = phi_inst->getIncomingValueForBlock(frame.m_prev_bb);
+                lldb_private::Scalar result;
+                if (!frame.EvaluateValue(result, value, module))
+                {
+                    if (log)
+                        log->Printf("Couldn't evaluate %s", PrintValue(value).c_str());
+                    error.SetErrorToGenericError();
+                    error.SetErrorString(bad_value_error);
+                    return false;
+                }
+                frame.AssignValue(inst, result, module);
+
+                if (log)
+                {
+                    log->Printf("Interpreted a %s", inst->getOpcodeName());
+                    log->Printf("  Incoming value : %s", frame.SummarizeValue(value).c_str());
+                }
+            }
+            break;
             case Instruction::GetElementPtr:
             {
                 const GetElementPtrInst *gep_inst = dyn_cast<GetElementPtrInst>(inst);
 
                 if (!gep_inst)
                 {
                     if (log)
                         log->Printf("getOpcode() returns GetElementPtr, but instruction is not a GetElementPtrInst");