From 136b54374551ff71a68772c89b180752914ea83e Mon Sep 17 00:00:00 2001
From: Guy Blank <guy.blank@intel.com>
Date: Thu, 10 Aug 2017 14:09:50 +0000
Subject: [PATCH] [SelectionDAG] Allow constant folding for implicitly
 truncating BUILD_VECTOR nodes.

In FoldConstantArithmetic, handle BUILD_VECTOR nodes that do implicit truncation on the elements.

This is similar to what is done in FoldConstantVectorArithmetic.

Differential Revision:
https://reviews.llvm.org/D36506

llvm-svn: 310593
---
 llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp | 18 ++++++++++++++++--
 llvm/test/CodeGen/X86/avx512-intrinsics.ll     |  2 --
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index c052bc64d7d8..a4a6562e33a9 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -3968,18 +3968,31 @@ SDValue SelectionDAG::FoldConstantArithmetic(unsigned Opcode, const SDLoc &DL,
   assert(BV1->getNumOperands() == BV2->getNumOperands() && "Out of sync!");
 
   EVT SVT = VT.getScalarType();
+  EVT LegalSVT = SVT;
+  if (NewNodesMustHaveLegalTypes && LegalSVT.isInteger()) {
+    LegalSVT = TLI->getTypeToTransformTo(*getContext(), LegalSVT);
+    if (LegalSVT.bitsLT(SVT))
+      return SDValue();
+  }
   SmallVector<SDValue, 4> Outputs;
   for (unsigned I = 0, E = BV1->getNumOperands(); I != E; ++I) {
     SDValue V1 = BV1->getOperand(I);
     SDValue V2 = BV2->getOperand(I);
 
-    // Avoid BUILD_VECTOR nodes that perform implicit truncation.
-    // FIXME: This is valid and could be handled by truncation.
+    if (SVT.isInteger()) {
+        if (V1->getValueType(0).bitsGT(SVT))
+          V1 = getNode(ISD::TRUNCATE, DL, SVT, V1);
+        if (V2->getValueType(0).bitsGT(SVT))
+          V2 = getNode(ISD::TRUNCATE, DL, SVT, V2);
+    }
+
     if (V1->getValueType(0) != SVT || V2->getValueType(0) != SVT)
       return SDValue();
 
     // Fold one vector element.
     SDValue ScalarResult = getNode(Opcode, DL, SVT, V1, V2);
+    if (LegalSVT != SVT)
+      ScalarResult = getNode(ISD::SIGN_EXTEND, DL, LegalSVT, ScalarResult);
 
     // Scalar folding only succeeded if the result is a constant or UNDEF.
     if (!ScalarResult.isUndef() && ScalarResult.getOpcode() != ISD::Constant &&
@@ -3998,6 +4011,7 @@ SDValue SelectionDAG::FoldConstantArithmetic(unsigned Opcode, const SDLoc &DL,
   return getBuildVector(VT, SDLoc(), Outputs);
 }
 
+// TODO: Merge with FoldConstantArithmetic
 SDValue SelectionDAG::FoldConstantVectorArithmetic(unsigned Opcode,
                                                    const SDLoc &DL, EVT VT,
                                                    ArrayRef<SDValue> Ops,
diff --git a/llvm/test/CodeGen/X86/avx512-intrinsics.ll b/llvm/test/CodeGen/X86/avx512-intrinsics.ll
index 737f0d18ee20..c80bf8ff15e6 100644
--- a/llvm/test/CodeGen/X86/avx512-intrinsics.ll
+++ b/llvm/test/CodeGen/X86/avx512-intrinsics.ll
@@ -123,8 +123,6 @@ define i16 @test_kxnor(i16 %a0, i16 %a1) {
 ; CHECK-NEXT:    kmovw %eax, %k2
 ; CHECK-NEXT:    kxorw %k0, %k1, %k0
 ; CHECK-NEXT:    kxorw %k0, %k2, %k0
-; CHECK-NEXT:    kxnorw %k0, %k0, %k1
-; CHECK-NEXT:    kxnorw %k1, %k0, %k0
 ; CHECK-NEXT:    kmovw %k0, %eax
 ; CHECK-NEXT:    ## kill: %AX<def> %AX<kill> %EAX<kill>
 ; CHECK-NEXT:    retq