Fix PR13991: legalizing an overflowing multiplication operation is harder than

the add/sub case since in the case of multiplication you also have to check that
the operation in the larger type did not overflow.

llvm-svn: 165017

llvm/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp

@@ -644,8 +644,9 @@ SDValue DAGTypeLegalizer::PromoteIntRes_XMULO(SDNode *N, unsigned ResNo) {
   EVT SmallVT = LHS.getValueType();
 
   // To determine if the result overflowed in a larger type, we extend the
-  // input to the larger type, do the multiply, then check the high bits of
+  // input to the larger type, do the multiply (checking if it overflows),
-  // the result to see if the overflow happened.
+  // then also check the high bits of the result to see if overflow happened
+  // there.
   if (N->getOpcode() == ISD::SMULO) {
     LHS = SExtPromotedInteger(LHS);
     RHS = SExtPromotedInteger(RHS);
@@ -653,24 +654,31 @@ SDValue DAGTypeLegalizer::PromoteIntRes_XMULO(SDNode *N, unsigned ResNo) {
     LHS = ZExtPromotedInteger(LHS);
     RHS = ZExtPromotedInteger(RHS);
   }
-  SDValue Mul = DAG.getNode(ISD::MUL, DL, LHS.getValueType(), LHS, RHS);
+  SDVTList VTs = DAG.getVTList(LHS.getValueType(), N->getValueType(1));
+  SDValue Mul = DAG.getNode(N->getOpcode(), DL, VTs, LHS, RHS);
 
-  // Overflow occurred iff the high part of the result does not
+  // Overflow occurred if it occurred in the larger type, or if the high part
-  // zero/sign-extend the low part.
+  // of the result does not zero/sign-extend the low part.  Check this second
+  // possibility first.
   SDValue Overflow;
   if (N->getOpcode() == ISD::UMULO) {
-    // Unsigned overflow occurred iff the high part is non-zero.
+    // Unsigned overflow occurred if the high part is non-zero.
     SDValue Hi = DAG.getNode(ISD::SRL, DL, Mul.getValueType(), Mul,
                              DAG.getIntPtrConstant(SmallVT.getSizeInBits()));
     Overflow = DAG.getSetCC(DL, N->getValueType(1), Hi,
                             DAG.getConstant(0, Hi.getValueType()), ISD::SETNE);
   } else {
-    // Signed overflow occurred iff the high part does not sign extend the low.
+    // Signed overflow occurred if the high part does not sign extend the low.
     SDValue SExt = DAG.getNode(ISD::SIGN_EXTEND_INREG, DL, Mul.getValueType(),
                                Mul, DAG.getValueType(SmallVT));
     Overflow = DAG.getSetCC(DL, N->getValueType(1), SExt, Mul, ISD::SETNE);
   }
 
+  // The only other way for overflow to occur is if the multiplication in the
+  // larger type itself overflowed.
+  Overflow = DAG.getNode(ISD::OR, DL, N->getValueType(1), Overflow,
+                         SDValue(Mul.getNode(), 1));
+
   // Use the calculated overflow everywhere.
   ReplaceValueWith(SDValue(N, 1), Overflow);
   return Mul;

llvm/test/CodeGen/X86/smul-with-overflow.ll

@@ -67,3 +67,17 @@ entry:
 ; CHECK: mull
 ; CHECK-NEXT: ret
 }
+
+declare { i63, i1 } @llvm.smul.with.overflow.i63(i63, i63) nounwind readnone
+
+define i1 @test5() nounwind {
+entry:
+  %res = call { i63, i1 } @llvm.smul.with.overflow.i63(i63 4, i63 4611686018427387903)
+  %sum = extractvalue { i63, i1 } %res, 0
+  %overflow = extractvalue { i63, i1 } %res, 1
+  ret i1 %overflow
+; Was returning false, should return true (not constant folded yet though).
+; PR13991
+; CHECK: test5:
+; CHECK-NOT: xorb
+}