tooling: add tools/compare_v_performance_between_commits

easily compare v performance/size across commits.

* fix eprintln on linux (it now uses stderr, and flushes it).

* flag: cleaner usage information.

tools/compare_v_performance_between_commits

@@ -0,0 +1,98 @@
+#!/bin/sh
+
+set -e 
+
+msg() { 
+    printf '%s\n' "$*"; 
+}
+
+if [ $# -ne 2 ]; then
+    msg "Usage: compare_v_to_c_performance COMMIT_BEFORE COMMIT_AFTER"
+    exit 1
+fi
+
+depend_on() { 
+    type "$1" >/dev/null 2>&1 || {
+        printf 'ERR: missing tool "%s"\n' "$1" >&2; exit 1;
+    } 
+}
+
+depend_on sh
+depend_on cp
+depend_on rm
+depend_on wc
+depend_on head
+depend_on cc
+depend_on strip
+depend_on git
+depend_on upx
+depend_on make
+depend_on hyperfine
+
+######################################################################
+## NB: cc should be a working, recent, sane C99 compiler 
+##     cc is used by the Makefile to bootstrap v (both gcc/clang work)
+##
+## If you are a C/V developer in a unix environment, you most probably 
+## already have the above installed, with the possible exception of:
+## https://github.com/sharkdp/hyperfine
+##
+## Installing them is out of scope of this tool.
+######################################################################
+
+COMMIT_B="$1"
+COMMIT_A="$2"
+
+CWD="$(pwd)"
+WORKDIR="/tmp"
+
+B="$WORKDIR/v_at_$COMMIT_B"
+A="$WORKDIR/v_at_$COMMIT_A"
+
+prepare_v() {
+    msg 
+    msg "Cloning current v source to $1 ..."
+    git clone --quiet "$CWD" "$1"
+    
+    cd "$1"
+    git checkout --quiet "$2"
+    
+    msg "Making v and vprod compilers in $1"
+    make > /dev/null
+    ./v -o v compiler 
+    ./v -prod -o vprod compiler
+    cp v     v_stripped 
+    cp vprod vprod_stripped 
+    strip *_stripped
+    cp v_stripped      v_stripped_upxed
+    cp vprod_stripped  vprod_stripped_upxed
+    upx -qqq --lzma v_stripped_upxed 
+    upx -qqq --lzma vprod_stripped_upxed
+    wc -c "$1/v" "$1/v_stripped" "$1/v_stripped_upxed" "$1/vprod" "$1/vprod_stripped" "$1/vprod_stripped_upxed" | head -n -1
+    VVERSION="$($1/v --version)"
+    GVERSION="$(git rev-parse --short  --verify HEAD)"
+    msg "V version is: $VVERSION , local source commit: $GVERSION"
+}
+
+compare_v_performance() {
+    CMD="$1"
+    msg "---------------------------------------------------------------------------------"
+    msg "Compare '$CMD'"
+    hyperfine --warmup=3 "cd '$B/' && $CMD "  "cd '$A/' && $CMD "
+    msg
+}
+
+##############################################################################
+# Cleanup artifacts from previous runs of this tool:
+cd "$WORKDIR"
+rm -rf "$A/" "$B/"
+##############################################################################
+
+msg "Comparing v compiler performance of commit $COMMIT_B (before) vs commit $COMMIT_A (after) ..."
+prepare_v "$B" "$COMMIT_B"
+prepare_v "$A" "$COMMIT_A"
+
+cd "$WORKDIR"
+compare_v_performance "./v     -o x.c compiler"
+compare_v_performance "./vprod -o x.c compiler"
+compare_v_performance "./vprod -o x   compiler"