[CodeGen] Fix result type for SMULO/UMULO legalization

[pftbest]

Summary

On some platforms (like MSP430) the second element of the result
structure for SMULO/UMULO may have a shorter type than the one
returned by SetCC. We need to truncate it to the right type, or
else some incorrect code may be generated later on.

This fixes issue https://github.com/rust-lang/rust/issues/37829

[pftbest]

Check if types are different before truncate

[efriedma]

lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

3521 ↗

(On Diff #79413)

Isn't OType just TopHalf.getType()?

3523 ↗

(On Diff #79413)

Please add an assertion that RType.getSizeInBits() <= OType.getSizeInBits(), just in case someone runs into it.

[pftbest]

Added an assertion, and also getting the size in bits from TopHalf directly

[efriedma]

LGTM.

[pftbest]

I don't have access to svn, so please commit it for me.

[pftbest]

ping

llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

if (isSigned) {
           TLI.getShiftAmountTy(BottomHalf.getValueType(), DAG.getDataLayout()));
       Tmp1 = DAG.getNode(ISD::SRA, dl, VT, BottomHalf, Tmp1);
       TopHalf = DAG.getSetCC(dl, getSetCCResultType(VT), TopHalf, Tmp1,
                              ISD::SETNE);
     } else {
       TopHalf = DAG.getSetCC(dl, getSetCCResultType(VT), TopHalf,
                              DAG.getConstant(0, dl, VT), ISD::SETNE);
     }
+
+    // Truncate the result if SetCC returns a larger type than needed.
+    EVT RType = Node->getValueType(1);
+    if (RType.getSizeInBits() < TopHalf.getValueSizeInBits())
+      TopHalf = DAG.getNode(ISD::TRUNCATE, dl, RType, TopHalf);
+
+    assert(RType.getSizeInBits() == TopHalf.getValueSizeInBits() &&
+           "Unexpected result type for S/UMULO legalization");
+
     Results.push_back(BottomHalf);
     Results.push_back(TopHalf);
     break;
   }
   case ISD::BUILD_PAIR: {
     EVT PairTy = Node->getValueType(0);
     Tmp1 = DAG.getNode(ISD::ZERO_EXTEND, dl, PairTy, Node->getOperand(0));
     Tmp2 = DAG.getNode(ISD::ANY_EXTEND, dl, PairTy, Node->getOperand(1));

llvm/trunk/test/CodeGen/MSP430/umulo-16.ll

+; RUN: llc < %s -march=msp430 | FileCheck %s
+target datalayout = "e-m:e-p:16:16-i32:16:32-a:16-n8:16"
+target triple = "msp430"
+
+define void @foo(i16 %arg) unnamed_addr {
+entry-block:
+  br i1 undef, label %bb2, label %bb3
+
+bb2:                                              ; preds = %entry-block
+  unreachable
+
+bb3:                                              ; preds = %entry-block
+  %0 = call { i16, i1 } @llvm.umul.with.overflow.i16(i16 undef, i16 %arg)
+; CHECK: call
+  %1 = extractvalue { i16, i1 } %0, 1
+  %2 = call i1 @llvm.expect.i1(i1 %1, i1 false)
+  br i1 %2, label %panic, label %bb5
+
+bb5:                                              ; preds = %bb3
+  unreachable
+
+panic:                                            ; preds = %bb3
+  unreachable
+}
+
+; Function Attrs: nounwind readnone
+declare i1 @llvm.expect.i1(i1, i1) #0
+
+; Function Attrs: nounwind readnone
+declare { i16, i1 } @llvm.umul.with.overflow.i16(i16, i16) #0
+
+attributes #0 = { nounwind readnone }