[meta] Use a ref-counted pointer to an InstructionFormat in instructions;

This avoids a lot of dereferences, and InstructionFormat are immutable
once they're created. It removes a lot of code that was keeping the
FormatRegistry around, just in case we needed the format. This is more
in line with the way we create Instructions, and make it easy to
reference InstructionFormats in general.

cranelift/codegen/meta/src/cdsl/instructions.rs

@@ -6,9 +6,7 @@ use std::fmt::{Display, Error, Formatter};
 use std::rc::Rc;
 
 use crate::cdsl::camel_case;
-use crate::cdsl::formats::{
-    FormatField, FormatRegistry, InstructionFormat, InstructionFormatIndex,
-};
+use crate::cdsl::formats::{FormatField, FormatRegistry, InstructionFormat};
 use crate::cdsl::operands::Operand;
 use crate::cdsl::type_inference::Constraint;
 use crate::cdsl::types::{LaneType, ReferenceType, ValueType, VectorType};
@@ -104,7 +102,7 @@ pub(crate) struct InstructionContent {
     pub constraints: Vec<Constraint>,
 
     /// Instruction format, automatically derived from the input operands.
-    pub format: InstructionFormatIndex,
+    pub format: Rc<InstructionFormat>,
 
     /// One of the input or output operands is a free type variable. None if the instruction is not
     /// polymorphic, set otherwise.
@@ -321,8 +319,7 @@ impl InstructionBuilder {
             .filter_map(|(i, op)| if op.is_value() { Some(i) } else { None })
             .collect();
 
-        let format_index = format_registry.lookup(&operands_in);
-        let format = format_registry.get(format_index);
+        let format = format_registry.lookup(&operands_in).clone();
         let polymorphic_info =
             verify_polymorphic(&operands_in, &operands_out, &format, &value_opnums);
 
@@ -339,7 +336,7 @@ impl InstructionBuilder {
             operands_in,
             operands_out,
             constraints: self.constraints.unwrap_or_else(Vec::new),
-            format: format_index,
+            format,
             polymorphic_info,
             value_opnums,
             value_results,
@@ -1093,9 +1090,9 @@ impl InstructionPredicate {
     }
 
     pub fn new_is_colocated_data(format_registry: &FormatRegistry) -> InstructionPredicateNode {
-        let format = format_registry.get(format_registry.by_name("UnaryGlobalValue"));
+        let format = format_registry.by_name("UnaryGlobalValue");
         InstructionPredicateNode::FormatPredicate(FormatPredicateNode::new(
-            format,
+            &*format,
             "global_value",
             FormatPredicateKind::IsColocatedData,
         ))