Revert "[DAGCombiner] Allow zextended load combines."

Breaks some bots.

1 files changed, 17 insertions, 56 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 71ee8e141bf..fb7ddf5b233 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -6750,6 +6750,12 @@ SDValue DAGCombiner::MatchLoadCombine(SDNode *N) {
     return SDValue();
   unsigned ByteWidth = VT.getSizeInBits() / 8;
 
+  // Before legalize we can introduce too wide illegal loads which will be later
+  // split into legal sized loads. This enables us to combine i64 load by i8
+  // patterns to a couple of i32 loads on 32 bit targets.
+  if (LegalOperations && !TLI.isOperationLegal(ISD::LOAD, VT))
+    return SDValue();
+
   bool IsBigEndianTarget = DAG.getDataLayout().isBigEndian();
   auto MemoryByteOffset = [&] (ByteProvider P) {
     assert(P.isMemory() && "Must be a memory byte provider");
@@ -6772,21 +6778,11 @@ SDValue DAGCombiner::MatchLoadCombine(SDNode *N) {
   // Check if all the bytes of the OR we are looking at are loaded from the same
   // base address. Collect bytes offsets from Base address in ByteOffsets.
   SmallVector<int64_t, 8> ByteOffsets(ByteWidth);
-  unsigned ZeroExtendedBytes = 0;
-  for (int i = ByteWidth - 1; i >= 0; --i) {
+  for (unsigned i = 0; i < ByteWidth; i++) {
     auto P = calculateByteProvider(SDValue(N, 0), i, 0, /*Root=*/true);
-    if (!P)
+    if (!P || !P->isMemory()) // All the bytes must be loaded from memory
       return SDValue();
 
-    if (P->isConstantZero()) {
-      // It's OK for the N most significant bytes to be 0, we can just
-      // zero-extend the load.
-      if (++ZeroExtendedBytes != (ByteWidth - static_cast<unsigned>(i)))
-        return SDValue();
-      continue;
-    }
-    assert(P->isMemory() && "provenance should either be memory or zero");
-
     LoadSDNode *L = P->Load;
     assert(L->hasNUsesOfValue(1, 0) && L->isSimple() &&
            !L->isIndexed() &&
@@ -6825,23 +6821,9 @@ SDValue DAGCombiner::MatchLoadCombine(SDNode *N) {
   assert(Base && "Base address of the accessed memory location must be set");
   assert(FirstOffset != INT64_MAX && "First byte offset must be set");
 
-  bool NeedsZext = ZeroExtendedBytes > 0;
-
-  EVT MemVT =
-      EVT::getIntegerVT(*DAG.getContext(), (ByteWidth - ZeroExtendedBytes) * 8);
-
-  // Before legalize we can introduce too wide illegal loads which will be later
-  // split into legal sized loads. This enables us to combine i64 load by i8
-  // patterns to a couple of i32 loads on 32 bit targets.
-  if (LegalOperations &&
-      !TLI.isOperationLegal(NeedsZext ? ISD::ZEXTLOAD : ISD::NON_EXTLOAD,
-                            MemVT))
-    return SDValue();
-
   // Check if the bytes of the OR we are looking at match with either big or
   // little endian value load
-  Optional<bool> IsBigEndian = isBigEndian(
-      makeArrayRef(ByteOffsets).drop_back(ZeroExtendedBytes), FirstOffset);
+  Optional<bool> IsBigEndian = isBigEndian(ByteOffsets, FirstOffset);
   if (!IsBigEndian.hasValue())
     return SDValue();
 
@@ -6854,8 +6836,7 @@ SDValue DAGCombiner::MatchLoadCombine(SDNode *N) {
   LoadSDNode *FirstLoad = FirstByteProvider->Load;
 
   // The node we are looking at matches with the pattern, check if we can
-  // replace it with a single (possibly zero-extended) load and bswap + shift if
-  // needed.
+  // replace it with a single load and bswap if needed.
 
   // If the load needs byte swap check if the target supports it
   bool NeedsBswap = IsBigEndianTarget != *IsBigEndian;
@@ -6863,45 +6844,25 @@ SDValue DAGCombiner::MatchLoadCombine(SDNode *N) {
   // Before legalize we can introduce illegal bswaps which will be later
   // converted to an explicit bswap sequence. This way we end up with a single
   // load and byte shuffling instead of several loads and byte shuffling.
-  // We do not introduce illegal bswaps when zero-extending as this tends to
-  // introduce too many arithmetic instructions.
-  if (NeedsBswap && (LegalOperations || NeedsZext) &&
-      !TLI.isOperationLegal(ISD::BSWAP, VT))
-    return SDValue();
-
-  // If we need to bswap and zero extend, we have to insert a shift. Check that
-  // it is legal.
-  if (NeedsBswap && NeedsZext && LegalOperations &&
-      !TLI.isOperationLegal(ISD::SHL, VT))
+  if (NeedsBswap && LegalOperations && !TLI.isOperationLegal(ISD::BSWAP, VT))
     return SDValue();
 
   // Check that a load of the wide type is both allowed and fast on the target
   bool Fast = false;
-  bool Allowed =
-      TLI.allowsMemoryAccess(*DAG.getContext(), DAG.getDataLayout(), MemVT,
-                             *FirstLoad->getMemOperand(), &Fast);
+  bool Allowed = TLI.allowsMemoryAccess(*DAG.getContext(), DAG.getDataLayout(),
+                                        VT, *FirstLoad->getMemOperand(), &Fast);
   if (!Allowed || !Fast)
     return SDValue();
 
-  SDValue NewLoad = DAG.getExtLoad(NeedsZext ? ISD::ZEXTLOAD : ISD::NON_EXTLOAD,
-                                   SDLoc(N), VT, Chain, FirstLoad->getBasePtr(),
-                                   FirstLoad->getPointerInfo(), MemVT,
-                                   FirstLoad->getAlignment());
+  SDValue NewLoad =
+      DAG.getLoad(VT, SDLoc(N), Chain, FirstLoad->getBasePtr(),
+                  FirstLoad->getPointerInfo(), FirstLoad->getAlignment());
 
   // Transfer chain users from old loads to the new load.
   for (LoadSDNode *L : Loads)
     DAG.ReplaceAllUsesOfValueWith(SDValue(L, 1), SDValue(NewLoad.getNode(), 1));
 
-  if (!NeedsBswap)
-    return NewLoad;
-
-  SDValue ShiftedLoad =
-      NeedsZext
-          ? DAG.getNode(ISD::SHL, SDLoc(N), VT, NewLoad,
-                        DAG.getShiftAmountConstant(ZeroExtendedBytes * 8, VT,
-                                                   SDLoc(N), LegalOperations))
-          : NewLoad;
-  return DAG.getNode(ISD::BSWAP, SDLoc(N), VT, ShiftedLoad);
+  return NeedsBswap ? DAG.getNode(ISD::BSWAP, SDLoc(N), VT, NewLoad) : NewLoad;
 }
 
 // If the target has andn, bsl, or a similar bit-select instruction,