Bitcast of 64-bit immediates may need to split the immediate, not a var.

tests_lit/llvm2ice_tests/bitcast.ll

 ; Trivial smoke test of bitcast between integer and FP types.
 
 ; RUN: %llvm2ice -O2 --verbose none %s | FileCheck %s
 ; RUN: %llvm2ice --verbose none %s | FileCheck --check-prefix=ERRORS %s
 ; RUN: %llvm2iceinsts %s | %szdiff %s | FileCheck --check-prefix=DUMP %s
 ; RUN: %llvm2iceinsts --pnacl %s | %szdiff %s \
 ; RUN:                           | FileCheck --check-prefix=DUMP %s
 
 define internal i32 @cast_f2i(float %f) {
 entry:
   %v0 = bitcast float %f to i32
   ret i32 %v0
 }
-
+; CHECK-LABEL: cast_f2i
 ; CHECK: mov eax
 ; CHECK: ret
 
 define internal float @cast_i2f(i32 %i) {
 entry:
   %v0 = bitcast i32 %i to float
   ret float %v0
 }
-
+; CHECK-LABEL: cast_i2f
 ; CHECK: fld dword ptr
 ; CHECK: ret
 
 define internal i64 @cast_d2ll(double %d) {
 entry:
   %v0 = bitcast double %d to i64
   ret i64 %v0
 }
-
+; CHECK-LABEL: cast_d2ll
 ; CHECK: mov edx
 ; CHECK: ret
 
+define internal i64 @cast_d2ll_const() {
+entry:
+  %v0 = bitcast double 0x12345678901234 to i64
+  ret i64 %v0
+}
+; CHECK-LABEL: cast_d2ll_const
+; CHECK: movsd xmm{{.*}}, {{.*}}L$double
+; CHECK: mov edx
+; CHECK: ret
+
 define internal double @cast_ll2d(i64 %ll) {
 entry:
   %v0 = bitcast i64 %ll to double
   ret double %v0
 }
-
+; CHECK-LABEL: cast_ll2d
 ; CHECK: fld qword ptr
 ; CHECK: ret
 
+define internal double @cast_ll2d_const() {
+entry:
+  %v0 = bitcast i64 12345678901234 to double
+  ret double %v0
+}
+; CHECK-LABEL: cast_ll2d_const
+; CHECK: mov {{.*}}, 1942892530
+; CHECK: mov {{.*}}, 2874
+; CHECK: fld qword ptr
+; CHECK: ret
+
 ; ERRORS-NOT: ICE translation error
 ; DUMP-NOT: SZ