[DAGCombiner][X86] When promoting loads don't use ZEXTLOAD even its legal

We were previously prefering ZEXTLOAD over EXTLOAD if it is legal. This triggers during X86's promotion of i16->i32. Not sure about other targets.

Using ZEXTLOAD can prevent folding it to SEXTLOAD later if we were to promote a sign extended operand like we would need for SRA. However, X86 doesn't currently promote i16 SRA. I was looking into doing that which is how I found this issue.

This is also blocking our ability to fold 4 byte aligned EXTLOADs with "loadi32". This is what caused most of the test changes here.

Differential Revision: https://reviews.llvm.org/D45585#inline-402825

llvm-svn: 330781

1 files changed, 4 insertions, 8 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 45c6e9771a3..e123e814c66 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1089,10 +1089,8 @@ SDValue DAGCombiner::PromoteOperand(SDValue Op, EVT PVT, bool &Replace) {
   if (ISD::isUNINDEXEDLoad(Op.getNode())) {
     LoadSDNode *LD = cast<LoadSDNode>(Op);
     EVT MemVT = LD->getMemoryVT();
-    ISD::LoadExtType ExtType = ISD::isNON_EXTLoad(LD)
-      ? (TLI.isLoadExtLegal(ISD::ZEXTLOAD, PVT, MemVT) ? ISD::ZEXTLOAD
-                                                       : ISD::EXTLOAD)
-      : LD->getExtensionType();
+    ISD::LoadExtType ExtType = ISD::isNON_EXTLoad(LD) ? ISD::EXTLOAD
+                                                      : LD->getExtensionType();
     Replace = true;
     return DAG.getExtLoad(ExtType, DL, PVT,
                           LD->getChain(), LD->getBasePtr(),
@@ -1327,10 +1325,8 @@ bool DAGCombiner::PromoteLoad(SDValue Op) {
     SDNode *N = Op.getNode();
     LoadSDNode *LD = cast<LoadSDNode>(N);
     EVT MemVT = LD->getMemoryVT();
-    ISD::LoadExtType ExtType = ISD::isNON_EXTLoad(LD)
-      ? (TLI.isLoadExtLegal(ISD::ZEXTLOAD, PVT, MemVT) ? ISD::ZEXTLOAD
-                                                       : ISD::EXTLOAD)
-      : LD->getExtensionType();
+    ISD::LoadExtType ExtType = ISD::isNON_EXTLoad(LD) ? ISD::EXTLOAD
+                                                      : LD->getExtensionType();
     SDValue NewLD = DAG.getExtLoad(ExtType, DL, PVT,
                                    LD->getChain(), LD->getBasePtr(),
                                    MemVT, LD->getMemOperand());