Use lowerCast instead of inlined _movzx, to get legalization, for memset.

tests_lit/llvm2ice_tests/nacl-other-intrinsics.ll

 ; This tests the NaCl intrinsics not related to atomic operations.
 
 ; RUN: %llvm2ice -O2 --verbose none %s | FileCheck %s
 ; RUN: %llvm2ice -Om1 --verbose none %s | FileCheck %s
 
 ; Do another run w/ O2 and a different check-prefix (otherwise O2 and Om1
 ; share the same "CHECK" prefix). This separate run helps check that
 ; some code is optimized out.
 ; RUN: %llvm2ice -O2 --verbose none %s | FileCheck %s --check-prefix=CHECKO2REM
 
@@ skipping 114 matching lines @@
 
 define void @test_memset(i32 %iptr_dst, i32 %wide_val, i32 %len) {
 entry:
   %val = trunc i32 %wide_val to i8
   %dst = inttoptr i32 %iptr_dst to i8*
   call void @llvm.memset.p0i8.i32(i8* %dst, i8 %val,
                                   i32 %len, i32 1, i1 0)
   ret void
 }
 ; CHECK-LABEL: test_memset
+; CHECK: movzx
 ; CHECK: call memset
 
 define void @test_memset_const_len_align(i32 %iptr_dst, i32 %wide_val) {
 entry:
   %val = trunc i32 %wide_val to i8
   %dst = inttoptr i32 %iptr_dst to i8*
   call void @llvm.memset.p0i8.i32(i8* %dst, i8 %val,
                                   i32 8, i32 1, i1 0)
   ret void
 }
 ; CHECK-LABEL: test_memset_const_len_align
+; CHECK: movzx
+; CHECK: call memset
+
+define void @test_memset_const_val(i32 %iptr_dst, i32 %len) {
+entry:
+  %dst = inttoptr i32 %iptr_dst to i8*
+  call void @llvm.memset.p0i8.i32(i8* %dst, i8 0, i32 %len, i32 1, i1 0)
+  ret void
+}
+; CHECK-LABEL: test_memset_const_val
+; Make sure the argument is legalized (can't movzx reg, 0).
+; CHECK: movzx {{.*}}, {{[^0]}}
 ; CHECK: call memset
 
 define i32 @test_setjmplongjmp(i32 %iptr_env) {
 entry:
   %env = inttoptr i32 %iptr_env to i8*
   %i = call i32 @llvm.nacl.setjmp(i8* %env)
   %r1 = icmp eq i32 %i, 0
   br i1 %r1, label %Zero, label %NonZero
 Zero:
   ; Redundant inttoptr, to make --pnacl cast-eliding/re-insertion happy.
@@ skipping 280 matching lines @@
 }
 ; CHECK-LABEL: test_stacksave_multiple
 ; At least 3 copies of esp, but probably more from having to do the allocas.
 ; CHECK: mov {{.*}}, esp
 ; CHECK: mov {{.*}}, esp
 ; CHECK: mov {{.*}}, esp
 ; CHECK: mov esp, {{.*}}
 
 ; ERRORS-NOT: ICE translation error
 ; DUMP-NOT: SZ