Fix for logic in combineExtract() (#108208)

A (csmith) test case appeared where combineExtract() crashed when the
input vector was a bitcast into a vector of i1:s. Fix this by adding a check
with canTreatAsByteVector() before the call.

Author: JonPsson1

llvm/lib/Target/SystemZ/SystemZISelLowering.cpp

@@ -7361,8 +7361,9 @@ SDValue SystemZTargetLowering::combineEXTRACT_VECTOR_ELT(
   if (auto *IndexN = dyn_cast<ConstantSDNode>(N->getOperand(1))) {
     SDValue Op0 = N->getOperand(0);
     EVT VecVT = Op0.getValueType();
-    return combineExtract(SDLoc(N), N->getValueType(0), VecVT, Op0,
-                          IndexN->getZExtValue(), DCI, false);
+    if (canTreatAsByteVector(VecVT))
+      return combineExtract(SDLoc(N), N->getValueType(0), VecVT, Op0,
+                            IndexN->getZExtValue(), DCI, false);
   }
   return SDValue();
 }

llvm/test/CodeGen/SystemZ/DAGCombine_extract_vector_elt.ll

@@ -0,0 +1,20 @@
+; RUN: llc -mtriple=s390x-linux-gnu -mcpu=z16 < %s  | FileCheck %s
+;
+; Check that DAGCombiner doesn't crash in SystemZ combineExtract()
+; when handling EXTRACT_VECTOR_ELT with a vector of i1:s.
+
+define i32 @fun(i32 %arg) {
+; CHECK-LABEL: fun:
+entry:
+  %cc = icmp eq i32 %arg, 0
+  br label %loop
+
+loop:
+  %P = phi <128 x i1> [ zeroinitializer, %entry ], [ bitcast (<2 x i64> <i64 3, i64 3> to <128 x i1>), %loop ]
+  br i1 %cc, label %exit, label %loop
+
+exit:
+  %E = extractelement <128 x i1> %P, i64 0
+  %Res = zext i1 %E to i32
+  ret i32 %Res
+}