[DAGCombiner] Avoid calling method 'isShuffleMaskLegal' on illegal vector types.

This patch fixes a crasher in method 'DAGCombiner::visitOR' due to an invalid
call to method 'isShuffleMaskLegal'. On x86, method 'isShuffleMaskLegal'
always expects a legal vector value type in input.

With this patch, we immediately check if the input OR dag node has a legal
vector type; we only try to fold a OR dag node into a single shufflevector
if we know that the resulting shuffle will have a legal type.
This is to avoid calling method 'isShuffleMaskLegal' on a potentially
illegal vector value type.

Added a new test-case to file 'CodeGen/X86/combine-or.ll' to verify that
DAGCombiner doesn't crash in the attempt to check/combine an OR between shuffles
with illegal types.

llvm-svn: 213020

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -3255,6 +3255,8 @@ SDValue DAGCombiner::visitOR(SDNode *N) {
     // Do this only if the resulting shuffle is legal.
     if (isa<ShuffleVectorSDNode>(N0) &&
         isa<ShuffleVectorSDNode>(N1) &&
+        // Avoid folding a node with illegal type.
+        TLI.isTypeLegal(VT) &&
         N0->getOperand(1) == N1->getOperand(1) &&
         ISD::isBuildVectorAllZeros(N0.getOperand(1).getNode())) {
       bool CanFold = true;

llvm/test/CodeGen/X86/combine-or.ll

@@ -266,4 +266,16 @@ define <2 x i64> @test21(<2 x i64> %a, <2 x i64> %b) {
 ; CHECK-NEXT: pslldq
 ; CHECK-NEXT: ret
 
+; Verify that the DAGCombiner doesn't crash in the attempt to check if a shuffle
+; with illegal type has a legal mask. Method 'isShuffleMaskLegal' only knows how to
+; handle legal vector value types.
+define <4 x i8> @test_crash(<4 x i8> %a, <4 x i8> %b) {
+  %shuf1 = shufflevector <4 x i8> %a, <4 x i8> zeroinitializer, <4 x i32><i32 4, i32 4, i32 2, i32 3>
+  %shuf2 = shufflevector <4 x i8> %b, <4 x i8> zeroinitializer, <4 x i32><i32 0, i32 1, i32 4, i32 4>
+  %or = or <4 x i8> %shuf1, %shuf2
+  ret <4 x i8> %or
+}
+; CHECK-LABEL: test_crash
+; CHECK: movsd
+; CHECK: ret