[X86] Ensure concat(blendi(),blendi()) -> vselect() uses legal select mask types

For 256-bit selections, we could be using sub-i8/vXi8 selection condition masks - extend these to i8 and then extract the lowest mask subvector

Fixes #132844

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -58617,10 +58617,13 @@ static SDValue combineConcatVectorOps(const SDLoc &DL, MVT VT,
           APInt Mask = getBLENDIBlendMask(Ops[0]).zext(NumElts);
           for (unsigned I = 1; I != NumOps; ++I)
             Mask.insertBits(getBLENDIBlendMask(Ops[I]), I * (NumElts / NumOps));
-          MVT MaskSVT = MVT::getIntegerVT(NumElts);
-          MVT MaskVT = MVT::getVectorVT(MVT::i1, NumElts);
+          unsigned NumMaskBits = NumElts >= 8 ? NumElts : 8;
+          Mask = Mask.zextOrTrunc(NumMaskBits);
+          MVT MaskSVT = MVT::getIntegerVT(NumMaskBits);
+          MVT MaskVT = MVT::getVectorVT(MVT::i1, NumMaskBits);
           SDValue Sel =
               DAG.getBitcast(MaskVT, DAG.getConstant(Mask, DL, MaskSVT));
+          Sel = extractSubVector(Sel, 0, DAG, DL, NumElts);
           Concat0 = Concat0 ? Concat0 : ConcatSubOperand(VT, Ops, 0);
           Concat1 = Concat1 ? Concat1 : ConcatSubOperand(VT, Ops, 1);
           return DAG.getSelect(DL, VT, Sel, Concat1, Concat0);

llvm/test/CodeGen/X86/pr132844.ll

@@ -0,0 +1,32 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc < %s -mtriple=x86_64-- -mcpu=x86-64-v4 | FileCheck %s
+
+define  { ptr, i8 } @PR132844(<4 x ptr> %0, <4 x ptr> %1) {
+; CHECK-LABEL: PR132844:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vextracti128 $1, %ymm0, %xmm2
+; CHECK-NEXT:    vinserti128 $1, %xmm0, %ymm1, %ymm0
+; CHECK-NEXT:    movb $10, %al
+; CHECK-NEXT:    kmovd %eax, %k1
+; CHECK-NEXT:    vinserti64x2 $1, 16, %ymm2, %ymm0 {%k1}
+; CHECK-NEXT:    vmovdqu %ymm0, {{[0-9]+}}(%rsp)
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    xorl %edx, %edx
+; CHECK-NEXT:    vzeroupper
+; CHECK-NEXT:    retq
+  %3 = alloca [35 x ptr], i32 0, align 16
+  %4 = load <4 x ptr>, ptr null, align 8
+  %5 = getelementptr i8, ptr %3, i64 216
+  %6 = extractelement <4 x ptr> %4, i64 3
+  store ptr %6, ptr %5, align 8
+  %7 = getelementptr i8, ptr %3, i64 208
+  %8 = extractelement <4 x ptr> %0, i64 0
+  store ptr %8, ptr %7, align 8
+  %9 = getelementptr i8, ptr %3, i64 200
+  %10 = extractelement <4 x ptr> %0, i64 3
+  store ptr %10, ptr %9, align 8
+  %11 = getelementptr i8, ptr %3, i64 192
+  %12 = extractelement <4 x ptr> %1, i64 0
+  store ptr %12, ptr %11, align 8
+  ret { ptr, i8 } zeroinitializer
+}