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.

2 files changed, 3 insertions, 3 deletions

diff --git a/compiler/rustc_codegen_llvm/src/abi.rs b/compiler/rustc_codegen_llvm/src/abi.rs
index 4b07c8aef91..009e7e2487b 100644
--- a/compiler/rustc_codegen_llvm/src/abi.rs
+++ b/compiler/rustc_codegen_llvm/src/abi.rs
@@ -146,7 +146,7 @@ impl LlvmType for CastTarget {
                 "total size {:?} cannot be divided into units of zero size",
                 self.rest.total
             );
-            if self.rest.total.bytes() % self.rest.unit.size.bytes() != 0 {
+            if !self.rest.total.bytes().is_multiple_of(self.rest.unit.size.bytes()) {
                 assert_eq!(self.rest.unit.kind, RegKind::Integer, "only int regs can be split");
             }
             self.rest.total.bytes().div_ceil(self.rest.unit.size.bytes())
diff --git a/compiler/rustc_codegen_llvm/src/va_arg.rs b/compiler/rustc_codegen_llvm/src/va_arg.rs
index 4fe4c9bcbf2..486dc894a4e 100644
--- a/compiler/rustc_codegen_llvm/src/va_arg.rs
+++ b/compiler/rustc_codegen_llvm/src/va_arg.rs
@@ -172,10 +172,10 @@ fn emit_aapcs_va_arg<'ll, 'tcx>(
 
     let gr_type = target_ty.is_any_ptr() || target_ty.is_integral();
     let (reg_off, reg_top, slot_size) = if gr_type {
-        let nreg = (layout.size.bytes() + 7) / 8;
+        let nreg = layout.size.bytes().div_ceil(8);
         (gr_offs, gr_top, nreg * 8)
     } else {
-        let nreg = (layout.size.bytes() + 15) / 16;
+        let nreg = layout.size.bytes().div_ceil(16);
         (vr_offs, vr_top, nreg * 16)
     };