pulley: Add macro instructions for function prologue/epilogue

This commit adds two new instructions to Pulley to combine the
operations of setting up a frame, allocating stack, and saving clobbered
registers. This is all combined into a single instruction which is
relatively large but is much smaller than each of these individual
operations exploded out.

This is a size win on `spidermonkey.cwasm` by about 1M and locally in a
small `fib.wat` test this is also a good speedup by reducing the number
of instructions executed.

cranelift/bitset/src/scalar.rs

@@ -556,14 +556,17 @@ pub trait ScalarBitSetStorage:
 macro_rules! impl_storage {
     ( $int:ty ) => {
         impl ScalarBitSetStorage for $int {
+            #[inline]
             fn leading_zeros(self) -> u8 {
                 u8::try_from(self.leading_zeros()).unwrap()
             }
 
+            #[inline]
             fn trailing_zeros(self) -> u8 {
                 u8::try_from(self.trailing_zeros()).unwrap()
             }
 
+            #[inline]
             fn count_ones(self) -> u8 {
                 u8::try_from(self.count_ones()).unwrap()
             }

cranelift/codegen/meta/src/pulley.rs

@@ -69,6 +69,10 @@ impl Inst<'_> {
                     Operand::Binop { dst, src1, src2 }
                 }
                 ("dst", ty) => Operand::Writable { name, ty },
+                (name, "RegSet < XReg >") => Operand::Normal {
+                    name,
+                    ty: "XRegSet",
+                },
                 (name, ty) => Operand::Normal { name, ty },
             })
             .chain(if self.name.contains("Trap") {
@@ -120,10 +124,17 @@ pub fn generate_rust(filename: &str, out_dir: &Path) -> Result<(), Error> {
                     if i > 0 {
                         format_string.push_str(",");
                     }
+
+                    if ty == "XRegSet" {
+                        format_string.push_str(" {");
+                        format_string.push_str(name);
+                        format_string.push_str(":?}");
+                        continue;
+                    }
+
                     format_string.push_str(" {");
                     format_string.push_str(name);
                     format_string.push_str("}");
-
                     if ty.contains("Reg") {
                         if name == "dst" {
                             locals.push_str(&format!("let {name} = reg_name(*{name}.to_reg());\n"));
@@ -176,6 +187,12 @@ pub fn generate_rust(filename: &str, out_dir: &Path) -> Result<(), Error> {
         let mut defs = Vec::new();
         for op in inst.operands() {
             match op {
+                // `{Push,Pop}FrameSave` doesn't participate in register allocation.
+                Operand::Normal {
+                    name: _,
+                    ty: "XRegSet",
+                } if *name == "PushFrameSave" || *name == "PopFrameSave" => {}
+
                 Operand::Normal { name, ty } => {
                     if ty.contains("Reg") {
                         uses.push(name);