Implement halving add idiom (with checker tests).

Rationale:
First of several idioms that map to very efficient SIMD instructions.
Note that the is-zero-ext and is-sign-ext are general-purpose utilities
that will be widely used in the vectorizer to detect low precision
idioms, so expect that code to be shared with many CLs to come.

Test: test-art-host, test-art-target
Change-Id: If7dc2926c72a2e4b5cea15c44ef68cf5503e9be9
diff --git a/compiler/optimizing/code_generator_vector_x86.cc b/compiler/optimizing/code_generator_vector_x86.cc
index 8dabb4d..a86d060 100644
--- a/compiler/optimizing/code_generator_vector_x86.cc
+++ b/compiler/optimizing/code_generator_vector_x86.cc
@@ -350,6 +350,35 @@
   }
 }
 
+void LocationsBuilderX86::VisitVecHalvingAdd(HVecHalvingAdd* instruction) {
+  CreateVecBinOpLocations(GetGraph()->GetArena(), instruction);
+}
+
+void InstructionCodeGeneratorX86::VisitVecHalvingAdd(HVecHalvingAdd* instruction) {
+  LocationSummary* locations = instruction->GetLocations();
+  DCHECK(locations->InAt(0).Equals(locations->Out()));
+  XmmRegister src = locations->InAt(1).AsFpuRegister<XmmRegister>();
+  XmmRegister dst = locations->Out().AsFpuRegister<XmmRegister>();
+
+  DCHECK(instruction->IsRounded());
+  DCHECK(instruction->IsUnsigned());
+
+  switch (instruction->GetPackedType()) {
+    case Primitive::kPrimByte:
+      DCHECK_EQ(16u, instruction->GetVectorLength());
+     __ pavgb(dst, src);
+     return;
+    case Primitive::kPrimChar:
+    case Primitive::kPrimShort:
+      DCHECK_EQ(8u, instruction->GetVectorLength());
+      __ pavgw(dst, src);
+      return;
+    default:
+      LOG(FATAL) << "Unsupported SIMD type";
+      UNREACHABLE();
+  }
+}
+
 void LocationsBuilderX86::VisitVecSub(HVecSub* instruction) {
   CreateVecBinOpLocations(GetGraph()->GetArena(), instruction);
 }
@@ -448,6 +477,22 @@
   }
 }
 
+void LocationsBuilderX86::VisitVecMin(HVecMin* instruction) {
+  CreateVecBinOpLocations(GetGraph()->GetArena(), instruction);
+}
+
+void InstructionCodeGeneratorX86::VisitVecMin(HVecMin* instruction) {
+  LOG(FATAL) << "No SIMD for " << instruction->GetId();
+}
+
+void LocationsBuilderX86::VisitVecMax(HVecMax* instruction) {
+  CreateVecBinOpLocations(GetGraph()->GetArena(), instruction);
+}
+
+void InstructionCodeGeneratorX86::VisitVecMax(HVecMax* instruction) {
+  LOG(FATAL) << "No SIMD for " << instruction->GetId();
+}
+
 void LocationsBuilderX86::VisitVecAnd(HVecAnd* instruction) {
   CreateVecBinOpLocations(GetGraph()->GetArena(), instruction);
 }