[PATCH] D17950: Implement is_always_lock_free

[James Y Knight via cfe-commits]

jyknight added inline comments.

================
Comment at: lib/Frontend/InitPreprocessor.cpp:305
@@ +304,3 @@
+    if (TypeWidth == TypeAlign && (TypeWidth & (TypeWidth - 1)) == 0 &&
+        TypeWidth <= InlineWidth)
+      return Always;
----------------
jfb wrote:
> bcraig wrote:
> > On some targets (like Hexagon), 4-byte values are cheap to inline, but 1-byte values are not.  Clang is spotty about checking this, but TargetInfo::hasBuiltinAtomic seems like the right function to ask, if you have access to it.
> You're commenting on:
> ```
>     if (TypeWidth == TypeAlign && (TypeWidth & (TypeWidth - 1)) == 0 &&
>         TypeWidth <= InlineWidth)
> ```
> ?
> 
> Are you asking for a separate change, or for a change to my patch?
That issue in clang's purview in any case; if hexagon wants to lower a 1-byte cmpxchg to a compiler runtime function, it should do so in its backend.


http://reviews.llvm.org/D17950