Prevent bogus return when constant fold does not happen.

Rather then return the correct result I believe we do not hit this
issue because the input has been restricted to constants that we
know can be constant folded and so I've replace the broken code with
an assert, which is in keeping with the other code in this area that
requires constant folding to work.

Author: paulwalker-arm

llvm/lib/Analysis/ConstantFolding.cpp

@@ -200,10 +200,10 @@ Constant *FoldBitCast(Constant *C, Type *DestTy, const DataLayout &DL) {
         IntegerType::get(C->getContext(), FPWidth), NumSrcElt);
     // Ask IR to do the conversion now that #elts line up.
     C = ConstantExpr::getBitCast(C, SrcIVTy);
-    // If IR wasn't able to fold it, bail out.
-    if (!isa<ConstantVector>(C) &&  // FIXME: Remove ConstantVector.
-        !isa<ConstantDataVector>(C))
-      return C;
+    assert((isa<ConstantVector>(C) || // FIXME: Remove ConstantVector.
+            isa<ConstantDataVector>(C) || isa<ConstantInt>(C) ||
+            isa<ConstantFP>(C)) &&
+           "Constant folding cannot fail for plain fp->int bitcast!");
   }
 
   // Now we know that the input and output vectors are both integer vectors

llvm/test/Transforms/InstSimplify/bitcast-vector-fold.ll

@@ -284,3 +284,11 @@ define <1 x i32> @bitcast_constexpr_scalar_fp_to_vector_int() {
   %res = bitcast float 1.0 to <1 x i32>
   ret <1 x i32> %res
 }
+
+define <2 x i64> @bitcast_constexpr_4f32_2i64_1111() {
+; CHECK-LABEL: @bitcast_constexpr_4f32_2i64_1111(
+; CHECK-NEXT:    ret <2 x i64> splat (i64 4575657222473777152)
+;
+  %res = bitcast <4 x float> splat (float 1.0) to <2 x i64>
+  ret <2 x i64> %res
+}