Rollup merge of #143477 - folkertdev:use-is-multiple-of, r=joshtriplett

use `is_multiple_of` and `div_ceil`

In tricky logic, these functions are much more informative than the manual implementations. They also catch subtle bugs:

- the manual `is_multiple_of` often does not handle division by zero
- manual `div_ceil` often does not consider overflow

The transformation is free for `is_multiple_of` if the divisor is compile-time known to be non-zero. For `div_ceil` there is a small cost to considering overflow. Here is some assembly https://godbolt.org/z/5zP8KaE1d.

1 files changed, 2 insertions, 2 deletions

diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs
index ff822b52a8d..c97d53a45de 100644
--- a/compiler/rustc_const_eval/src/interpret/memory.rs
+++ b/compiler/rustc_const_eval/src/interpret/memory.rs
@@ -537,7 +537,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
         #[inline]
         fn is_offset_misaligned(offset: u64, align: Align) -> Option<Misalignment> {
-            if offset % align.bytes() == 0 {
+            if offset.is_multiple_of(align.bytes()) {
                 None
             } else {
                 // The biggest power of two through which `offset` is divisible.
@@ -1554,7 +1554,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                         // If the allocation is N-aligned, and the offset is not divisible by N,
                         // then `base + offset` has a non-zero remainder after division by `N`,
                         // which means `base + offset` cannot be null.
-                        if offset.bytes() % info.align.bytes() != 0 {
+                        if !offset.bytes().is_multiple_of(info.align.bytes()) {
                             return interp_ok(false);
                         }
                         // We don't know enough, this might be null.