[SVE] Fix warnings in SelectInst::areInvalidOperands

[david-arm]

Summary

We should be comparing the element counts rather than the
numbers of elements.

[efriedma]

llvm/lib/IR/Instructions.cpp

84

We probably want a testcase to make sure we don't accept select <2 x i1> zeroinitializer, <vscale x 2 x i64> zeroinitializer, <vscale x 2 x i64> zeroinitializer

[efriedma]

LGTM

llvm/lib/IR/Instructions.cpp

const char *SelectInst::areInvalidOperands(Value *Op0, Value *Op1, Value *Op2) {
 
   if (VectorType *VT = dyn_cast<VectorType>(Op0->getType())) {
     // Vector select.
     if (VT->getElementType() != Type::getInt1Ty(Op0->getContext()))
       return "vector select condition element type must be i1";
     VectorType *ET = dyn_cast<VectorType>(Op1->getType());
     if (!ET)
       return "selected values for vector select must be vectors";
-    if (ET->getNumElements() != VT->getNumElements())
+    if (ET->getElementCount() != VT->getElementCount())
       return "vector select requires selected vectors to have "
                    "the same vector length as select condition";
   } else if (Op0->getType() != Type::getInt1Ty(Op0->getContext())) {
     return "select condition must be i1 or <n x i1>";
   }
   return nullptr;
 }
 

llvm/test/CodeGen/AArch64/sve-bad-select.ll

+; RUN: not llc -mtriple=aarch64-linux-gnu -mattr=+sve < %s 2>&1 | FileCheck %s
+
+define <vscale x 16 x i8> @badsel1_nxv16i8(<16 x i1> %p,
+                                           <vscale x 16 x i8> %dst,
+                                           <vscale x 16 x i8> %a) {
+  %sel = select <16 x i1> %p, <vscale x 16 x i8> %a, <vscale x 16 x i8> %dst
+  ret <vscale x 16 x i8> %sel
+}
+
+; CHECK: error: vector select requires selected vectors to have the same vector length as select condition