From: Tudor Bosman <tudorb@fb.com>
Date: Wed, 8 Aug 2012 21:08:03 +0000 (-0700)
Subject: Remove 1 instruction from popcount
X-Git-Tag: v0.22.0~1222
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=71acc41b44cb2f8a20cbf37a17f32a4eb7f7fc25;p=folly.git

Remove 1 instruction from popcount

Summary:
by removing the unnecessary constraint that the input and output be in
the same register (copypasta from https://phabricator.fb.com/D542718)

Test Plan: folly/test

Reviewed By: soren@fb.com

FB internal diff: D543310
---

diff --git a/folly/Bits.cpp b/folly/Bits.cpp
index 41c2bc46..1c825d2a 100644
--- a/folly/Bits.cpp
+++ b/folly/Bits.cpp
@@ -25,8 +25,9 @@
 namespace {
 
 int popcount_inst(unsigned int x) {
-  asm ("popcntl %0, %0" : "=r" (x) : "0" (x));
-  return x;
+  int n;
+  asm ("popcntl %1, %0" : "=r" (n) : "r" (x));
+  return n;
 }
 
 int popcount_builtin(unsigned int x) {
@@ -34,8 +35,9 @@ int popcount_builtin(unsigned int x) {
 }
 
 int popcountll_inst(unsigned long long x) {
-  asm ("popcntq %0, %0" : "=r" (x) : "0" (x));
-  return x;
+  unsigned long long n;
+  asm ("popcntq %1, %0" : "=r" (n) : "r" (x));
+  return n;
 }
 
 int popcountll_builtin(unsigned long long x) {