From 24562a9f49e06ce1cf62448911407dc6c4fd757e Mon Sep 17 00:00:00 2001
From: Johannes Altmanninger <aclopte@gmail.com>
Date: Mon, 16 Dec 2019 12:56:30 +0100
Subject: [PATCH] avoid allocation on lookup of $fish_trace

Looking up a variable by a string literal implicitly constructs a wcstring.
By avoiding that, we get a noticeable reduction of temporary allocations.

$ HOME=. heaptrack ./fish -c true
heaptrack stats:			# baseline
        allocations:            7635
        leaked allocations:     3277
        temporary allocations:  602
heaptrack stats:			# new
        allocations:            7565
        leaked allocations:     3267
        temporary allocations:  530
---
 src/trace.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/trace.cpp b/src/trace.cpp
index 03b6481db..d7968c9c4 100644
--- a/src/trace.cpp
+++ b/src/trace.cpp
@@ -6,11 +6,13 @@
 #include "flog.h"
 #include "parser.h"
 
+static const wcstring VAR_fish_trace = L"fish_trace";
+
 bool trace_enabled(const parser_t &parser) {
     auto &ld = parser.libdata();
     if (ld.suppress_fish_trace) return false;
     // TODO: this variable lookup is somewhat expensive, consider how to make this cheaper.
-    return !parser.vars().get(L"fish_trace").missing_or_empty();
+    return !parser.vars().get(VAR_fish_trace).missing_or_empty();
 }
 
 /// Trace an "argv": a list of arguments where the first is the command.