tests: add 3 cases involving pointers to codegen/transmute-scalar.

Author: eddyb

Diff for: src/test/codegen/transmute-scalar.rs

@@ -2,6 +2,9 @@
 
 #![crate_type = "lib"]
 
+// FIXME(eddyb) all of these tests show memory stores and loads, even after a
+// scalar `bitcast`, more special-casing is required to remove `alloca` usage.
+
 // CHECK: define i32 @f32_to_bits(float %x)
 // CHECK: %2 = bitcast float %x to i32
 // CHECK-NEXT: store i32 %2, i32* %0
@@ -33,3 +36,50 @@ pub fn bool_to_byte(b: bool) -> u8 {
 pub unsafe fn byte_to_bool(byte: u8) -> bool {
     std::mem::transmute(byte)
 }
+
+// CHECK: define i8* @ptr_to_ptr(i16* %p)
+// CHECK: %2 = bitcast i16* %p to i8*
+// CHECK-NEXT: store i8* %2, i8** %0
+// CHECK-NEXT: %3 = load i8*, i8** %0
+// CHECK: ret i8* %3
+#[no_mangle]
+pub fn ptr_to_ptr(p: *mut u16) -> *mut u8 {
+    unsafe { std::mem::transmute(p) }
+}
+
+// HACK(eddyb) scalar `transmute`s between pointers and non-pointers are
+// currently not special-cased like other scalar `transmute`s, because
+// LLVM requires specifically `ptrtoint`/`inttoptr` instead of `bitcast`.
+//
+// Tests below show the non-special-cased behavior (with the possible
+// future special-cased instructions in the "NOTE(eddyb)" comments).
+
+// CHECK: define [[USIZE:i[0-9]+]] @ptr_to_int(i16* %p)
+
+// NOTE(eddyb) see above, the following two CHECK lines should ideally be this:
+//        %2 = ptrtoint i16* %p to [[USIZE]]
+//             store [[USIZE]] %2, [[USIZE]]* %0
+// CHECK: %2 = bitcast [[USIZE]]* %0 to i16**
+// CHECK-NEXT: store i16* %p, i16** %2
+
+// CHECK-NEXT: %3 = load [[USIZE]], [[USIZE]]* %0
+// CHECK: ret [[USIZE]] %3
+#[no_mangle]
+pub fn ptr_to_int(p: *mut u16) -> usize {
+    unsafe { std::mem::transmute(p) }
+}
+
+// CHECK: define i16* @int_to_ptr([[USIZE]] %i)
+
+// NOTE(eddyb) see above, the following two CHECK lines should ideally be this:
+//        %2 = inttoptr [[USIZE]] %i to i16*
+//             store i16* %2, i16** %0
+// CHECK: %2 = bitcast i16** %0 to [[USIZE]]*
+// CHECK-NEXT: store [[USIZE]] %i, [[USIZE]]* %2
+
+// CHECK-NEXT: %3 = load i16*, i16** %0
+// CHECK: ret i16* %3
+#[no_mangle]
+pub fn int_to_ptr(i: usize) -> *mut u16 {
+    unsafe { std::mem::transmute(i) }
+}