MIR: Allow parsing of empty machine functions

If you run llc -stop-after=codegenprepare and feed the resulting MIR
to llc -start-after=codegenprepare, you'll have an empty machine
function since we haven't run any isel yet. Of course, this only works
if the MIRParser believes you that this is okay.

This is essentially a revert of r241862 with a fix for the problem it
was papering over.

llvm-svn: 299975

2 files changed, 4 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/MIRParser/MIRParser.cpp b/llvm/lib/CodeGen/MIRParser/MIRParser.cpp
index d1f5ed47d81..a2773cccc5d 100644
--- a/llvm/lib/CodeGen/MIRParser/MIRParser.cpp
+++ b/llvm/lib/CodeGen/MIRParser/MIRParser.cpp
@@ -367,9 +367,6 @@ bool MIRParserImpl::initializeMachineFunction(MachineFunction &MF) {
   }
   PFS.SM = &SM;
 
-  if (MF.empty())
-    return error(Twine("machine function '") + Twine(MF.getName()) +
-                 "' requires at least one machine basic block in its body");
   // Initialize the frame information after creating all the MBBs so that the
   // MBB references in the frame information can be resolved.
   if (initializeFrameInfo(PFS, YamlMF))
diff --git a/llvm/lib/CodeGen/MachineVerifier.cpp b/llvm/lib/CodeGen/MachineVerifier.cpp
index fc4026174ca..f49232b0f8a 100644
--- a/llvm/lib/CodeGen/MachineVerifier.cpp
+++ b/llvm/lib/CodeGen/MachineVerifier.cpp
@@ -528,7 +528,8 @@ void MachineVerifier::visitMachineFunctionBefore() {
   lastIndex = SlotIndex();
   regsReserved = MRI->getReservedRegs();
 
-  markReachable(&MF->front());
+  if (!MF->empty())
+    markReachable(&MF->front());
 
   // Build a set of the basic blocks in the function.
   FunctionBlocks.clear();
@@ -548,7 +549,8 @@ void MachineVerifier::visitMachineFunctionBefore() {
   // Check that the register use lists are sane.
   MRI->verifyUseLists();
 
-  verifyStackFrame();
+  if (!MF->empty())
+    verifyStackFrame();
 }
 
 // Does iterator point to a and b as the first two elements?