Integer legalization: fix MUL expansion

Summary:
This fixes the runtime results produces by the fallback multiplication expansion introduced in r270720.

For tests I created a fuzz tester that compares the results with Boost.Multiprecision.

Reviewers: hfinkel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D26628

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286998 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp

@@ -2230,7 +2230,7 @@ void DAGTypeLegalizer::ExpandIntRes_MUL(SDNode *N,
     SDValue RLH = DAG.getNode(ISD::SRL, dl, NVT, RL, Shift);
 
     SDValue U = DAG.getNode(ISD::ADD, dl, NVT,
-                            DAG.getNode(ISD::MUL, dl, NVT, LLH, RLL), TL);
+                            DAG.getNode(ISD::MUL, dl, NVT, LLH, RLL), TH);
     SDValue UL = DAG.getNode(ISD::AND, dl, NVT, U, Mask);
     SDValue UH = DAG.getNode(ISD::SRL, dl, NVT, U, Shift);
 
@@ -2239,9 +2239,9 @@ void DAGTypeLegalizer::ExpandIntRes_MUL(SDNode *N,
     SDValue VH = DAG.getNode(ISD::SRL, dl, NVT, V, Shift);
 
     SDValue W = DAG.getNode(ISD::ADD, dl, NVT,
-                            DAG.getNode(ISD::MUL, dl, NVT, LL, RL),
+                            DAG.getNode(ISD::MUL, dl, NVT, LLH, RLH),
                             DAG.getNode(ISD::ADD, dl, NVT, UH, VH));
-    Lo = DAG.getNode(ISD::ADD, dl, NVT, TH,
+    Lo = DAG.getNode(ISD::ADD, dl, NVT, TL,
                      DAG.getNode(ISD::SHL, dl, NVT, V, Shift));
 
     Hi = DAG.getNode(ISD::ADD, dl, NVT, W,

test/CodeGen/X86/mul-i256.ll

@@ -15,12 +15,17 @@ entry:
 ; There is a lot of inter-register motion, and so matching the instruction
 ; sequence will be fragile. There should be 6 underlying multiplications.
 ; CHECK: imulq
+; CHECK: mulq
 ; CHECK: imulq
 ; CHECK: imulq
+; CHECK: mulq
 ; CHECK: imulq
-; CHECK: imulq
-; CHECK: imulq
+; CHECK: mulq
+; CHECK: mulq
+; CHECK: mulq
+; CHECK: mulq
 ; CHECK-NOT: imulq
+; CHECK-NOT: mulq
 ; CHECK: retq
 
 attributes #0 = { norecurse nounwind uwtable "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" }