[llvm] r268972 - [X86][SSE] Improve cost model for i64 vector comparisons on pre-SSE42 targets

[Simon Pilgrim via llvm-commits]

Author: rksimon
Date: Mon May  9 16:14:38 2016
New Revision: 268972

URL: http://llvm.org/viewvc/llvm-project?rev=268972&view=rev
Log:
[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

Modified:
    llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp
    llvm/trunk/test/Analysis/CostModel/X86/cmp.ll

Modified: llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp?rev=268972&r1=268971&r2=268972&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp Mon May  9 16:14:38 2016
@@ -857,13 +857,17 @@ int X86TTIImpl::getCmpSelInstrCost(unsig
   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(unsig
     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);
 }
 

Modified: llvm/trunk/test/Analysis/CostModel/X86/cmp.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/CostModel/X86/cmp.ll?rev=268972&r1=268971&r2=268972&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/CostModel/X86/cmp.ll (original)
+++ llvm/trunk/test/Analysis/CostModel/X86/cmp.ll Mon May  9 16:14:38 2016
@@ -87,18 +87,18 @@ define i32 @cmp(i32 %arg) {
   ;AVX:   cost of 1 {{.*}} icmp
   %H = icmp eq <4 x i32> undef, undef
 
-  ;SSE2:  cost of 1 {{.*}} icmp
-  ;SSE3:  cost of 1 {{.*}} icmp
-  ;SSSE3: cost of 1 {{.*}} icmp
-  ;SSE41: cost of 1 {{.*}} icmp
+  ;SSE2:  cost of 8 {{.*}} icmp
+  ;SSE3:  cost of 8 {{.*}} icmp
+  ;SSSE3: cost of 8 {{.*}} icmp
+  ;SSE41: cost of 8 {{.*}} icmp
   ;SSE42: cost of 1 {{.*}} icmp
   ;AVX:   cost of 1 {{.*}} icmp
   %I = icmp eq <2 x i64> undef, undef
 
-  ;SSE2:  cost of 2 {{.*}} icmp
-  ;SSE3:  cost of 2 {{.*}} icmp
-  ;SSSE3: cost of 2 {{.*}} icmp
-  ;SSE41: cost of 2 {{.*}} icmp
+  ;SSE2:  cost of 16 {{.*}} icmp
+  ;SSE3:  cost of 16 {{.*}} icmp
+  ;SSSE3: cost of 16 {{.*}} icmp
+  ;SSE41: cost of 16 {{.*}} icmp
   ;SSE42: cost of 2 {{.*}} icmp
   ;AVX1:  cost of 4 {{.*}} icmp
   ;AVX2:  cost of 1 {{.*}} icmp