cranelift/reader/src/parser.rs: fn parse_inst_resuts: produce the results as a

SmallVec<[Value; 1]>, not as a Vec<Value>.  This isn't a useful change for any
non-developer use of Cranelift, but it does significantly reduce the amount of
allocation "noise" seen when tuning the new backend pipeline as driven by
clif-util reading .clif files.  In one case the number of malloc calls
declined by about 20% with this change.

Cargo.lock

@@ -489,6 +489,7 @@ name = "cranelift-reader"
 version = "0.63.0"
 dependencies = [
  "cranelift-codegen",
+ "smallvec",
  "target-lexicon",
  "thiserror",
 ]

cranelift/reader/Cargo.toml

@@ -11,6 +11,7 @@ edition = "2018"
 
 [dependencies]
 cranelift-codegen = { path = "../codegen", version = "0.63.0" }
+smallvec = "1.0.0"
 target-lexicon = "0.10"
 thiserror = "1.0.15"
 

cranelift/reader/src/parser.rs

@@ -23,6 +23,7 @@ use cranelift_codegen::ir::{
 use cranelift_codegen::isa::{self, CallConv, Encoding, RegUnit, TargetIsa};
 use cranelift_codegen::packed_option::ReservedValue;
 use cranelift_codegen::{settings, timing};
+use smallvec::SmallVec;
 use std::mem;
 use std::str::FromStr;
 use std::{u16, u32};
@@ -2223,9 +2224,9 @@ impl<'a> Parser<'a> {
     //
     // inst-results ::= Value(v) { "," Value(v) }
     //
-    fn parse_inst_results(&mut self) -> ParseResult<Vec<Value>> {
+    fn parse_inst_results(&mut self) -> ParseResult<SmallVec<[Value; 1]>> {
         // Result value numbers.
-        let mut results = Vec::new();
+        let mut results = SmallVec::new();
 
         // instruction  ::=  * [inst-results "="] Opcode(opc) ["." Type] ...
         // inst-results ::= * Value(v) { "," Value(v) }