[PATCH] D12271: [X86] Expose the various _rot intrinsics on non-MS platforms

[Reid Kleckner via cfe-commits]

rnk accepted this revision.
rnk added a comment.
This revision is now accepted and ready to land.

This looks good.

As a larger issue, LLVM fast isel definitely won't pattern match this series of shifts and selects to rotl at -O0. There are some users who want branchless constant time rotates regardless of optimization level (https://llvm.org/bugs/show_bug.cgi?id=24226). My thinking is that the shifts are more analyzable to LLVM than an intrinsic, so we should leave these intrinsics alone and tell such users to use inline asm if they need these kinds of low-level guarantees. It still isn't very satisfactory. =/


================
Comment at: test/CodeGen/x86-rot-intrinsics.c:9-11
@@ +8,5 @@
+#else
+// Don't include mm_malloc.h, it's system specific.
+#define __MM_MALLOC_H
+#include <immintrin.h>
+#endif
----------------
Any reason not to use -ffreestanding to deal with this on the Linux side of the test like we do for windows?


http://reviews.llvm.org/D12271