use (isub 1 $C) instead (iadd -1 $C)

cranelift/codegen/src/preopt.peepmatic

@@ -195,4 +195,4 @@
 ;; Reminder by a power of two -> bitwise and with decreased by one constant.
 (=> (when (urem_imm $C $x)
           (is-power-of-two $C))
-    (band_imm $(iadd -1 $C) $x))
+    (band_imm $(isub 1 $C) $x))

cranelift/peepmatic/crates/runtime/src/operator.rs

@@ -233,6 +233,10 @@ pub enum UnquoteOperator {
     #[peepmatic(params(iNN, iNN), result(iNN))]
     Iadd,
 
+    /// Compile-time `iadd` of two constant values.
+    #[peepmatic(params(iNN, iNN), result(iNN))]
+    Isub,
+
     /// Compile-time `imul` of two constant values.
     #[peepmatic(params(iNN, iNN), result(iNN))]
     Imul,

cranelift/peepmatic/crates/runtime/src/optimizer.rs

@@ -77,6 +77,7 @@ where
             | UnquoteOperator::Bor
             | UnquoteOperator::Bxor
             | UnquoteOperator::Iadd
+            | UnquoteOperator::Isub
             | UnquoteOperator::Imul => unreachable!("not a unary unquote operator: {:?}", operator),
         }
     }
@@ -98,6 +99,7 @@ where
             UnquoteOperator::Bor => fold_ints!(a, b, |x, y| x | y),
             UnquoteOperator::Bxor => fold_ints!(a, b, |x, y| x ^ y),
             UnquoteOperator::Iadd => fold_ints!(a, b, |x, y| x.wrapping_add(y)),
+            UnquoteOperator::Isub => fold_ints!(a, b, |x, y| x.wrapping_sub(y)),
             UnquoteOperator::Imul => fold_ints!(a, b, |x, y| x.wrapping_mul(y)),
             UnquoteOperator::Log2 | UnquoteOperator::Neg => {
                 unreachable!("not a binary unquote operator: {:?}", operator)