[InstCombine] remove overzealous assert for shuffles (PR41419)

As the TODO indicates, instsimplify could be improved.

Should fix:
https://bugs.llvm.org/show_bug.cgi?id=41419

llvm-svn: 357910
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index 665064c..28d5f18 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -1353,8 +1353,8 @@
   // Canonicalize to choose from operand 0 first.
   unsigned NumElts = Shuf.getType()->getVectorNumElements();
   if (Shuf.getMaskValue(0) >= (int)NumElts) {
-    assert(!isa<UndefValue>(Shuf.getOperand(1)) &&
-           "Not expecting undef shuffle operand with select mask");
+    // TODO: Can we assert that both operands of a shuffle-select are not undef
+    // (otherwise, it would have been folded by instsimplify?
     Shuf.commute();
     return &Shuf;
   }