From 94190d57244b26baf36629c88104b0ba516510cf Mon Sep 17 00:00:00 2001
From: Julian Seward <jseward@acm.org>
Date: Mon, 11 May 2020 11:09:40 +0200
Subject: [PATCH] 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                     | 1 +
 cranelift/reader/Cargo.toml    | 1 +
 cranelift/reader/src/parser.rs | 5 +++--
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 52c8ef1b89..71798731de 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -489,6 +489,7 @@ name = "cranelift-reader"
 version = "0.63.0"
 dependencies = [
  "cranelift-codegen",
+ "smallvec",
  "target-lexicon",
  "thiserror",
 ]
diff --git a/cranelift/reader/Cargo.toml b/cranelift/reader/Cargo.toml
index fb0f8a1fda..8b8b451bfd 100644
--- a/cranelift/reader/Cargo.toml
+++ b/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"
 
diff --git a/cranelift/reader/src/parser.rs b/cranelift/reader/src/parser.rs
index 4e9608a506..4a59a13667 100644
--- a/cranelift/reader/src/parser.rs
+++ b/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) }