[DAGCombiner] Don't allow addcarry if the type of the carry producer is illegal.

[jonpa]

Summary

getAsCarry() checks that the input argument is a carry-producing node before allowing a transformation to addcarry. This patch adds a check to make sure that the carry-producing node is legal. If it is not, it may not remain in a form that is manageable by the backend. The test case causes a compilation failure during instruction selection for this reason on SystemZ.

DAGCombine.cpp patch Patch by Ulrich Weigand.

[spatel]

LGTM

test/CodeGen/SystemZ/dag-combine-05.ll

9–10

It's better to use positive CHECK lines so we know the result is correct rather than only 'not wrong'.
'utils/update_llc_test_checks.py' should be fine to use here.

[jonpa]

Thanks for review! Test case updated per suggestion.

r357052

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

static SDValue getAsCarry(const TargetLowering &TLI, SDValue V) {
   // If this is not a carry, return.
   if (V.getResNo() != 1)
     return SDValue();
 
   if (V.getOpcode() != ISD::ADDCARRY && V.getOpcode() != ISD::SUBCARRY &&
       V.getOpcode() != ISD::UADDO && V.getOpcode() != ISD::USUBO)
     return SDValue();
 
+  EVT VT = V.getNode()->getValueType(0);
+  if (!TLI.isOperationLegalOrCustom(V.getOpcode(), VT))
+    return SDValue();
+
   // If the result is masked, then no matter what kind of bool it is we can
   // return. If it isn't, then we need to make sure the bool type is either 0 or
   // 1 and not other values.
   if (Masked ||
       TLI.getBooleanContents(V.getValueType()) ==
           TargetLoweringBase::ZeroOrOneBooleanContent)
     return V;
 

test/CodeGen/SystemZ/dag-combine-05.ll

+; Test that DAGCombiner does not produce an addcarry node if the carry
+; producer is not legal. This can happen e.g. with an uaddo with a type
+; that is not legal.
+;
+; RUN: llc -mtriple=s390x-linux-gnu -mcpu=z13 -debug-only=isel < %s 2>&1 \
+; RUN:   | FileCheck %s
+; REQUIRES: asserts
+
+; CHECK-NOT: addcarry
+; CHECK-NOT: LLVM ERROR: Cannot select: {{.*}} = SystemZISD::GET_CCMASK
+
+define void @fun(i16 %arg0, i16* %src, i32* %dst) {
+bb:
+  %tmp = icmp ult i16 %arg0, 9616
+  %tmp1 = zext i1 %tmp to i32
+  %tmp2 = load i16, i16* %src
+  %tmp3 = add i16 %tmp2, -1
+  %tmp4 = icmp ne i16 %tmp2, 0
+  %tmp5 = zext i1 %tmp4 to i32
+  %tmp6 = add nuw nsw i32 %tmp5, %tmp1
+  store i32 %tmp6, i32* %dst
+  ret void
+}