[X86][SSE] Improve cost model for i64 vector comparisons on pre-SSE42 targets

As discussed on PR24888, until SSE42 we don't have access to PCMPGTQ for v2i64 comparisons, but the cost models don't reflect this, resulting in over-optimistic vectorizaton.

This patch adds SSE2 'base level' costs that match what a typical target is capable of and only reduces the v2i64 costs at SSE42.

Technically SSE41 provides a PCMPEQQ v2i64 equality test, but as getCmpSelInstrCost doesn't give us a way to discriminate between comparison test types we can't easily make use of this, otherwise we could split the cost of integer equality and greater-than tests to give better costings of each.

Differential Revision: http://reviews.llvm.org/D20057

llvm-svn: 268972

1 files changed, 11 insertions, 3 deletions

diff --git a/llvm/lib/Target/X86/X86TargetTransformInfo.cpp b/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
index 6ffef1654ea..28ae96d4108 100644
--- a/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
+++ b/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
@@ -857,13 +857,17 @@ int X86TTIImpl::getCmpSelInstrCost(unsigned Opcode, Type *ValTy, Type *CondTy) {
   int ISD = TLI->InstructionOpcodeToISD(Opcode);
   assert(ISD && "Invalid opcode");
 
+  static const CostTblEntry SSE2CostTbl[] = {
+    { ISD::SETCC,   MVT::v2i64,   8 },
+    { ISD::SETCC,   MVT::v4i32,   1 },
+    { ISD::SETCC,   MVT::v8i16,   1 },
+    { ISD::SETCC,   MVT::v16i8,   1 },
+  };
+
   static const CostTblEntry SSE42CostTbl[] = {
     { ISD::SETCC,   MVT::v2f64,   1 },
     { ISD::SETCC,   MVT::v4f32,   1 },
     { ISD::SETCC,   MVT::v2i64,   1 },
-    { ISD::SETCC,   MVT::v4i32,   1 },
-    { ISD::SETCC,   MVT::v8i16,   1 },
-    { ISD::SETCC,   MVT::v16i8,   1 },
   };
 
   static const CostTblEntry AVX1CostTbl[] = {
@@ -906,6 +910,10 @@ int X86TTIImpl::getCmpSelInstrCost(unsigned Opcode, Type *ValTy, Type *CondTy) {
     if (const auto *Entry = CostTableLookup(SSE42CostTbl, ISD, MTy))
       return LT.first * Entry->Cost;
 
+  if (ST->hasSSE2())
+    if (const auto *Entry = CostTableLookup(SSE2CostTbl, ISD, MTy))
+      return LT.first * Entry->Cost;
+
   return BaseT::getCmpSelInstrCost(Opcode, ValTy, CondTy);
 }