Add bitwise ops that invert the second operand.

ARM has all of these as scalar integer instructions. Intel has band_not
in SSE and as a scalar in BMI1.

Add the trivial legalization patterns that use a bnot instruction.

cranelift/docs/langref.rst

@@ -667,11 +667,9 @@ operating on boolean values, the bitwise operations work as logical operators.
 .. autoinst:: bxor
 .. autoinst:: bxor_imm
 .. autoinst:: bnot
-
-.. todo:: Redundant bitwise operators.
-
-    ARM has instructions like ``bic(x,y) = x & ~y``, ``orn(x,y) = x | ~y``, and
-    ``eon(x,y) = x ^ ~y``.
+.. autoinst:: band_not
+.. autoinst:: bor_not
+.. autoinst:: bxor_not
 
 The shift and rotate operations only work on integer types (scalar and vector).
 The shift amount does not have to be the same type as the value being shifted.

cranelift/filetests/isa/riscv/expand-i32.cton

@@ -28,3 +28,11 @@ ebb0(v0: i32):
 ; check: $(cst=$V) = iconst.i32 0x3b9a_ca00
 ; check: $v1 = iadd $v0, $cst
 ; check: return $v1
+
+function %bitclear(i32, i32) -> i32 {
+ebb0(v0: i32, v1: i32):
+    v2 = band_not v0, v1
+    ; check: bnot
+    ; check: band
+    return v2
+}