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

1 files changed, 4 insertions, 2 deletions

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?