[GlobalISel]: Fix a bug where we could dereference None

getConstantVRegVal returns None when dealing with constants > 64 bits.
Don't assume we always have a value in GISelKnownBits.

llvm-svn: 371465

diff --git a/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp b/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
index 7db6465..c0391f7 100644 (file)
--- a/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
@@ -140,6 +140,8 @@ void GISelKnownBits::computeKnownBitsImpl(Register R, KnownBits &Known,
   }
   case TargetOpcode::G_CONSTANT: {
     auto CstVal = getConstantVRegVal(R, MRI);
+    if (!CstVal)
+      break;
     Known.One = *CstVal;
     Known.Zero = ~Known.One;
     break;