Index: lib/IR/ConstantFold.cpp
===================================================================
--- lib/IR/ConstantFold.cpp
+++ lib/IR/ConstantFold.cpp
@@ -191,6 +191,10 @@
     if (FP->getType()->isPPC_FP128Ty())
       return nullptr;
 
+    // Make sure dest type is compatible with the folded integer constant.
+    if (!DestTy->isIntegerTy())
+      return nullptr;
+
     return ConstantInt::get(FP->getContext(),
                             FP->getValueAPF().bitcastToAPInt());
   }
Index: test/CodeGen/X86/mmx-bitcast-fold.ll
===================================================================
--- /dev/null
+++ test/CodeGen/X86/mmx-bitcast-fold.ll
@@ -0,0 +1,12 @@
+; RUN: opt -mtriple=x86_64-- -early-cse < %s -S | FileCheck %s
+
+; CHECK: @foo(x86_mmx bitcast (double 0.000000e+00 to x86_mmx))
+
+define void @bar() {
+entry:
+  %0 = bitcast double 0.0 to x86_mmx
+  %1 = call x86_mmx @foo(x86_mmx %0)
+  ret void
+}
+
+declare x86_mmx @foo(x86_mmx)