From: Mainak Mandal <mmandal@fb.com>
Date: Wed, 26 Aug 2015 17:42:59 +0000 (-0700)
Subject: make doNotOptimizeAway work with clang
X-Git-Tag: v0.56.0~3
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=a3c67e006de0e32ecad1bc406ab74ca767e4caee;p=folly.git

make doNotOptimizeAway work with clang

Summary: Projects depending on benchmark library fail to build with clang with the following error
```
./folly/Benchark.h:263:16: error: inline asm not supported yet: don't know how to handle tied indirect register inputs
```

I am not an expert here, just tried to take an approach similar to the MSVC compiler clause

Reviewed By: @andralex, @yfeldblum

Differential Revision: D2368670
---

diff --git a/folly/Benchmark.h b/folly/Benchmark.h
index 3478d10f..c25ca280 100644
--- a/folly/Benchmark.h
+++ b/folly/Benchmark.h
@@ -257,11 +257,19 @@ void doNotOptimizeAway(T&& datum) {
 
 #pragma optimize("", on)
 
+#elif defined(__clang__)
+
+template <class T>
+__attribute__((__optnone__)) void doNotOptimizeAway(T&& datum) {
+}
+
 #else
+
 template <class T>
 void doNotOptimizeAway(T&& datum) {
   asm volatile("" : "+r" (datum));
 }
+
 #endif
 
 } // namespace folly