[x86] fix cost model inaccuracy for vector memory ops
The irony of this patch is that one CPU that is affected is AMD Jaguar, and Jaguar
has a completely double-pumped AVX implementation. But getting the cost model to
reflect that is a much bigger problem. The small goal here is simply to improve on
the lie that !AVX2 == SandyBridge.
Differential Revision: http://reviews.llvm.org/D18000
llvm-svn: 263069
diff --git a/llvm/lib/Target/X86/X86TargetTransformInfo.cpp b/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
index efa7feb..ba977eb 100644
--- a/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
+++ b/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
@@ -983,10 +983,10 @@
// Each load/store unit costs 1.
int Cost = LT.first * 1;
- // On Sandybridge 256bit load/stores are double pumped
- // (but not on Haswell).
- if (LT.second.getSizeInBits() > 128 && !ST->hasAVX2())
- Cost*=2;
+ // This isn't exactly right. We're using slow unaligned 32-byte accesses as a
+ // proxy for a double-pumped AVX memory interface such as on Sandybridge.
+ if (LT.second.getStoreSize() == 32 && ST->isUnalignedMem32Slow())
+ Cost *= 2;
return Cost;
}