[PATCH] D59822: [DAGCombiner] Don't allow addcarry if the type of the carry producer is illegal.

[Jonas Paulsson via Phabricator via llvm-commits]

jonpa created this revision.
jonpa added reviewers: uweigand, deadalnix, spatel.
Herald added a subscriber: jdoerfert.

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.


https://reviews.llvm.org/D59822

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  test/CodeGen/SystemZ/dag-combine-05.ll


Index: test/CodeGen/SystemZ/dag-combine-05.ll
===================================================================
--- /dev/null
+++ test/CodeGen/SystemZ/dag-combine-05.ll
@@ -0,0 +1,23 @@
+; 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
+}
Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2324,6 +2324,10 @@
       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.


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