Set both `nuw` and `nsw` in slice size calculation

There's an old note in the code to do this, and now that LLVM-C has an API for it, we might as well.

1 files changed, 29 insertions, 6 deletions

diff --git a/compiler/rustc_codegen_ssa/src/traits/builder.rs b/compiler/rustc_codegen_ssa/src/traits/builder.rs
index b7dcf16fa2b..871bf8b0d1b 100644
--- a/compiler/rustc_codegen_ssa/src/traits/builder.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/builder.rs
@@ -159,12 +159,35 @@ pub trait BuilderMethods<'a, 'tcx>:
     /// must be interpreted as unsigned and can be assumed to be less than the size of the left
     /// operand.
     fn ashr(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
-    fn unchecked_sadd(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
-    fn unchecked_uadd(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
-    fn unchecked_ssub(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
-    fn unchecked_usub(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
-    fn unchecked_smul(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
-    fn unchecked_umul(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
+    fn unchecked_sadd(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value {
+        self.add(lhs, rhs)
+    }
+    fn unchecked_uadd(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value {
+        self.add(lhs, rhs)
+    }
+    fn unchecked_suadd(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value {
+        self.unchecked_sadd(lhs, rhs)
+    }
+    fn unchecked_ssub(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value {
+        self.sub(lhs, rhs)
+    }
+    fn unchecked_usub(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value {
+        self.sub(lhs, rhs)
+    }
+    fn unchecked_susub(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value {
+        self.unchecked_ssub(lhs, rhs)
+    }
+    fn unchecked_smul(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value {
+        self.mul(lhs, rhs)
+    }
+    fn unchecked_umul(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value {
+        self.mul(lhs, rhs)
+    }
+    fn unchecked_sumul(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value {
+        // Which to default to is a fairly arbitrary choice,
+        // but this is what slice layout was using before.
+        self.unchecked_smul(lhs, rhs)
+    }
     fn and(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
     fn or(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
     /// Defaults to [`Self::or`], but guarantees `(lhs & rhs) == 0` so some backends