[x86] Simplify vector selection

[rob.khasanov]

Summary

[x86] Simplify vector selection if condition value type matches vselect value type and true value is all ones or false value is all zeros.
This transformation worked if selector is produced by SETCC, however SETCC is needed only if we consider to swap operands. So I replaced SETCC check for this case.
New tests are not added, existed intrinsics tests on vpcmpeq{bwdq} cover these cases.

[rob.khasanov]

Added a test case for VSELECT simplification.
Removed changes corresponding to intrinsics lowering, it will go as separate patch.

[rob.khasanov]

Added more test cases

[chandlerc]

Is this still relevant? A lot has changed w/ this part of LLVM since October.

lib/Target/X86/X86ISelLowering.cpp

if (Opc && NeedSplit) {
       RHS = DAG.getNode(Opc, DL, LHS2.getValueType(), LHS2, RHS2);
 
       // Merge the result
       return DAG.getNode(ISD::CONCAT_VECTORS, DL, VT, LHS, RHS);
     } else if (Opc)
       return DAG.getNode(Opc, DL, VT, LHS, RHS);
   }
 
-  // Simplify vector selection if the selector will be produced by CMPP*/PCMP*.
-  if (N->getOpcode() == ISD::VSELECT && Cond.getOpcode() == ISD::SETCC &&
-      // Check if SETCC has already been promoted
-      TLI.getSetCCResultType(*DAG.getContext(), VT) == CondVT &&
-      // Check that condition value type matches vselect operand type
-      CondVT == VT) { 
-
+  // Simplify vector selection if condition value type matches vselect
+  // operand type
+  if (N->getOpcode() == ISD::VSELECT && CondVT == VT) {
     assert(Cond.getValueType().isVector() &&
            "vector select expects a vector selector!");
 
     bool TValIsAllOnes = ISD::isBuildVectorAllOnes(LHS.getNode());
     bool FValIsAllZeros = ISD::isBuildVectorAllZeros(RHS.getNode());
 
-    if (!TValIsAllOnes && !FValIsAllZeros) {
-      // Try invert the condition if true value is not all 1s and false value
-      // is not all 0s.
+    if (!TValIsAllOnes && !FValIsAllZeros &&
+        // Check if the selector will be produced by CMPP*/PCMP*
+        Cond.getOpcode() == ISD::SETCC &&
+        // Check if SETCC has already been promoted
+        TLI.getSetCCResultType(*DAG.getContext(), VT) == CondVT) {
       bool TValIsAllZeros = ISD::isBuildVectorAllZeros(LHS.getNode());
       bool FValIsAllOnes = ISD::isBuildVectorAllOnes(RHS.getNode());
 
       if (TValIsAllZeros || FValIsAllOnes) {
         SDValue CC = Cond.getOperand(2);
         ISD::CondCode NewCC =
           ISD::getSetCCInverse(cast<CondCodeSDNode>(CC)->get(),
                                Cond.getOperand(0).getValueType().isInteger());

test/CodeGen/X86/avx512-select.ll

 ; CHECK-LABEL: @select04
 ; CHECK: vmovaps %zmm3, %zmm1
 ; CHECK-NEXT: ret
 ; PR20677
 define <16 x double> @select04(<16 x double> %a, <16 x double> %b) {
   %sel = select <16 x i1> <i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 false, i1 false, i1 false, i1 false, i1 false, i1 false, i1 false, i1 false>, <16 x double> %a, <16 x double> %b
   ret <16 x double> %sel
 }
+
+; CHECK-LABEL: select05
+; CHECK: kmovw   %esi, %k0
+; CHECK-NEXT: kmovw   %edi, %k1
+; CHECK-NEXT: korw    %k1, %k0, %k0
+; CHECK-NEXT: kmovw   %k0, %eax
+define i8 @select05 (i8 %a.0, i8 %m) {
+  %mask = bitcast i8 %m to <8 x i1>
+  %a = bitcast i8 %a.0 to <8 x i1>
+  %r = select <8 x i1> %mask, <8 x i1> <i1 -1, i1 -1, i1 -1, i1 -1, i1 -1, i1 -1, i1 -1, i1 -1>, <8 x i1> %a
+  %res = bitcast <8 x i1> %r to i8
+  ret i8 %res;
+}