[llvm] r263069 - [x86] fix cost model inaccuracy for vector memory ops

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Wed Mar  9 16:23:33 2016
New Revision: 263069

URL: http://llvm.org/viewvc/llvm-project?rev=263069&view=rev
Log:
[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


Modified:
    llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp
    llvm/trunk/test/Transforms/LoopVectorize/X86/avx1.ll

Modified: llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp?rev=263069&r1=263068&r2=263069&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp Wed Mar  9 16:23:33 2016
@@ -983,10 +983,10 @@ int X86TTIImpl::getMemoryOpCost(unsigned
   // 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;
 }

Modified: llvm/trunk/test/Transforms/LoopVectorize/X86/avx1.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/X86/avx1.ll?rev=263069&r1=263068&r2=263069&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopVectorize/X86/avx1.ll (original)
+++ llvm/trunk/test/Transforms/LoopVectorize/X86/avx1.ll Wed Mar  9 16:23:33 2016
@@ -26,10 +26,10 @@ define i32 @read_mod_write_single_ptr(fl
   ret i32 undef
 }
 
-;;; FIXME: If 32-byte accesses are fast, this should use a <4 x i64> load.
 
 ; CHECK-LABEL: @read_mod_i64(
-; CHECK: load <2 x i64>
+; SLOWMEM32: load <2 x i64>
+; FASTMEM32: load <4 x i64>
 ; CHECK: ret i32
 define i32 @read_mod_i64(i64* nocapture %a, i32 %n) nounwind uwtable ssp {
   %1 = icmp sgt i32 %n, 0