[PATCH] D107581: [LegalizeTypes] Add a simple expansion for SMULO when a libcall isn't available.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: efriedma, lebedev.ri, FreddyYe, erichkeane, skan, jtmott-intel, LuoYuanke.
Herald added a subscriber: hiraditya.
craig.topper requested review of this revision.
Herald added a project: LLVM.

This isn't optimal, but prevents crashing when the libcall isn't
available. It just calculates the full product and makes sure the high bits
match the sign of the low half. Each of the pieces should go through their own
type legalization.

This can make D107420 <https://reviews.llvm.org/D107420> unnecessary.

Needs tests, but I wanted to start discussion about D107420 <https://reviews.llvm.org/D107420>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D107581

Files:
  llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp


Index: llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
+++ llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
@@ -4035,7 +4035,25 @@
     LC = RTLIB::MULO_I64;
   else if (VT == MVT::i128)
     LC = RTLIB::MULO_I128;
-  assert(LC != RTLIB::UNKNOWN_LIBCALL && "Unsupported XMULO!");
+
+  if (LC == RTLIB::UNKNOWN_LIBCALL || !TLI.getLibcallName(LC)) {
+    // FIXME: This is not an optimal expansion, but better than crashing.
+    EVT WideVT =
+        EVT::getIntegerVT(*DAG.getContext(), VT.getScalarSizeInBits() * 2);
+    SDValue LHS = DAG.getNode(ISD::SIGN_EXTEND, dl, WideVT, N->getOperand(0));
+    SDValue RHS = DAG.getNode(ISD::SIGN_EXTEND, dl, WideVT, N->getOperand(1));
+    SDValue Mul = DAG.getNode(ISD::MUL, dl, WideVT, LHS, RHS);
+    SDValue MulLo, MulHi;
+    SplitInteger(Mul, MulLo, MulHi);
+    SDValue SRA =
+        DAG.getNode(ISD::SRA, dl, VT, MulLo,
+                    DAG.getConstant(VT.getScalarSizeInBits() - 1, dl, VT));
+    SDValue Overflow =
+        DAG.getSetCC(dl, N->getValueType(1), MulHi, SRA, ISD::SETNE);
+    SplitInteger(MulLo, Lo, Hi);
+    ReplaceValueWith(SDValue(N, 1), Overflow);
+    return;
+  }
 
   SDValue Temp = DAG.CreateStackTemporary(PtrVT);
   // Temporary for the overflow value, default it to zero.


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