[SystemZ] Add a check against zero before calling getTestUnderMaskCond()

Csmith discovered that this function can be called with a zero argument,
in which case an assert for this triggered.

This patch also adds a guard before the other call to this function since
it was missing, although the test only covers the case where it was
discovered.

Reduced test case attached as CodeGen/SystemZ/int-cmp-54.ll.

Review: Ulrich Weigand

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306287 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/SystemZ/SystemZISelLowering.cpp

@@ -2054,6 +2054,7 @@ static void adjustForTestUnderMask(SelectionDAG &DAG, const SDLoc &DL,
   if (NewC.ICmpType != SystemZICMP::SignedOnly &&
       NewC.Op0.getOpcode() == ISD::SHL &&
       isSimpleShift(NewC.Op0, ShiftVal) &&
+      (MaskVal >> ShiftVal != 0) &&
       (NewCCMask = getTestUnderMaskCond(BitSize, NewC.CCMask,
                                         MaskVal >> ShiftVal,
                                         CmpVal >> ShiftVal,
@@ -2063,6 +2064,7 @@ static void adjustForTestUnderMask(SelectionDAG &DAG, const SDLoc &DL,
   } else if (NewC.ICmpType != SystemZICMP::SignedOnly &&
              NewC.Op0.getOpcode() == ISD::SRL &&
              isSimpleShift(NewC.Op0, ShiftVal) &&
+             (MaskVal << ShiftVal != 0) &&
              (NewCCMask = getTestUnderMaskCond(BitSize, NewC.CCMask,
                                                MaskVal << ShiftVal,
                                                CmpVal << ShiftVal,

test/CodeGen/SystemZ/int-cmp-54.ll

@@ -0,0 +1,20 @@
+; Check that custom handling of SETCC does not crash
+;
+; RUN: llc < %s -mtriple=s390x-linux-gnu -mcpu=z13
+
+@g_39 = external global [4 x i8], align 2
+@g_2166 = external global <{ i8, i8, i8, i8, i8, i8, i8, i8, i8, i8, i8, i32 }>, align 8
+
+; Function Attrs: nounwind
+define void @main() local_unnamed_addr #0 {
+  %1 = load volatile i88, i88* bitcast (<{ i8, i8, i8, i8, i8, i8, i8, i8, i8, i8, i8, i32 }>* @g_2166 to i88*), align 8
+  %2 = lshr i88 %1, 87
+  %3 = trunc i88 %2 to i64
+  %4 = icmp sgt i64 %3, 9293
+  %5 = zext i1 %4 to i32
+  %6 = lshr i32 %5, 0
+  %7 = shl i32 %6, 6
+  %8 = trunc i32 %7 to i8
+  store i8 %8, i8* getelementptr inbounds ([4 x i8], [4 x i8]* @g_39, i64 0, i64 1), align 1
+  unreachable
+}