Revert "[WebAssembly] Combine i128 to v16i8 for setcc & expand memcmp for 16 byte loads with simd128" (#153360)

Reverts llvm/llvm-project#149461

The first test w/ memcmp in `test/neon/test_neon_wasm_simd.cpp` in the
Emscripten test suite has failed. This PR applies a revert so I can take
a closer look at it

Test case link:
https://github.com/emscripten-core/emscripten/blob/main/test/neon/test_neon_wasm_simd.cpp

Compile option: `em++ test_neon_wasm_simd.cpp -O2 -mfpu=neon -msimd128
-o something.js`

Original comment report:
llvm/llvm-project#149461 (comment)

Author: badumbatish

llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp

@@ -3383,65 +3383,15 @@ static SDValue TryMatchTrue(SDNode *N, EVT VecVT, SelectionDAG &DAG) {
   return DAG.getZExtOrTrunc(Ret, DL, N->getValueType(0));
 }
 
-/// Try to convert a i128 comparison to a v16i8 comparison before type
-/// legalization splits it up into chunks
-static SDValue
-combineVectorSizedSetCCEquality(SDNode *N, TargetLowering::DAGCombinerInfo &DCI,
-                                const WebAssemblySubtarget *Subtarget) {
-
-  SDLoc DL(N);
-  SDValue X = N->getOperand(0);
-  SDValue Y = N->getOperand(1);
-  EVT VT = N->getValueType(0);
-  EVT OpVT = X.getValueType();
-
-  SelectionDAG &DAG = DCI.DAG;
-  if (DCI.DAG.getMachineFunction().getFunction().hasFnAttribute(
-          Attribute::NoImplicitFloat))
-    return SDValue();
-
-  ISD::CondCode CC = cast<CondCodeSDNode>(N->getOperand(2))->get();
-  // We're looking for an oversized integer equality comparison with SIMD
-  if (!OpVT.isScalarInteger() || !OpVT.isByteSized() || OpVT != MVT::i128 ||
-      !Subtarget->hasSIMD128() || !isIntEqualitySetCC(CC))
-    return SDValue();
-
-  // Don't perform this combine if constructing the vector will be expensive.
-  auto IsVectorBitCastCheap = [](SDValue X) {
-    X = peekThroughBitcasts(X);
-    return isa<ConstantSDNode>(X) || X.getOpcode() == ISD::LOAD;
-  };
-
-  if (!IsVectorBitCastCheap(X) || !IsVectorBitCastCheap(Y))
-    return SDValue();
-
-  SDValue VecX = DAG.getBitcast(MVT::v16i8, X);
-  SDValue VecY = DAG.getBitcast(MVT::v16i8, Y);
-  SDValue Cmp = DAG.getSetCC(DL, MVT::v16i8, VecX, VecY, CC);
-
-  SDValue Intr =
-      DAG.getNode(ISD::INTRINSIC_WO_CHAIN, DL, MVT::i32,
-                  {DAG.getConstant(CC == ISD::SETEQ ? Intrinsic::wasm_alltrue
-                                                    : Intrinsic::wasm_anytrue,
-                                   DL, MVT::i32),
-                   Cmp});
-
-  return DAG.getSetCC(DL, VT, Intr, DAG.getConstant(0, DL, MVT::i32), CC);
-}
-
 static SDValue performSETCCCombine(SDNode *N,
-                                   TargetLowering::DAGCombinerInfo &DCI,
-                                   const WebAssemblySubtarget *Subtarget) {
+                                   TargetLowering::DAGCombinerInfo &DCI) {
   if (!DCI.isBeforeLegalize())
     return SDValue();
 
   EVT VT = N->getValueType(0);
   if (!VT.isScalarInteger())
     return SDValue();
 
-  if (SDValue V = combineVectorSizedSetCCEquality(N, DCI, Subtarget))
-    return V;
-
   SDValue LHS = N->getOperand(0);
   if (LHS->getOpcode() != ISD::BITCAST)
     return SDValue();
@@ -3621,7 +3571,7 @@ WebAssemblyTargetLowering::PerformDAGCombine(SDNode *N,
   case ISD::BITCAST:
     return performBitcastCombine(N, DCI);
   case ISD::SETCC:
-    return performSETCCCombine(N, DCI, Subtarget);
+    return performSETCCCombine(N, DCI);
   case ISD::VECTOR_SHUFFLE:
     return performVECTOR_SHUFFLECombine(N, DCI);
   case ISD::SIGN_EXTEND:

llvm/lib/Target/WebAssembly/WebAssemblyTargetTransformInfo.cpp

@@ -147,8 +147,7 @@ WebAssemblyTTIImpl::enableMemCmpExpansion(bool OptSize, bool IsZeroCmp) const {
 
   Options.AllowOverlappingLoads = true;
 
-  if (ST->hasSIMD128())
-    Options.LoadSizes.push_back(16);
+  // TODO: Teach WebAssembly backend about load v128.
 
   Options.LoadSizes.append({8, 4, 2, 1});
   Options.MaxNumLoads = TLI->getMaxExpandSizeMemcmp(OptSize);

llvm/test/CodeGen/WebAssembly/memcmp-expand.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
-; RUN: llc < %s  -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -mattr=+simd128 | FileCheck %s
+; RUN: llc < %s  -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers | FileCheck %s
 
 target triple = "wasm32-unknown-unknown"
 
@@ -127,16 +127,24 @@ define i1 @memcmp_expand_8(ptr %a, ptr %b) {
   ret i1 %res
 }
 
+; TODO: Should be using a single load i64x2 or equivalent in bitsizes
 define i1 @memcmp_expand_16(ptr %a, ptr %b) {
 ; CHECK-LABEL: memcmp_expand_16:
 ; CHECK:         .functype memcmp_expand_16 (i32, i32) -> (i32)
 ; CHECK-NEXT:  # %bb.0:
-; CHECK-NEXT:    v128.load $push1=, 0($0):p2align=0
-; CHECK-NEXT:    v128.load $push0=, 0($1):p2align=0
-; CHECK-NEXT:    i8x16.eq $push2=, $pop1, $pop0
-; CHECK-NEXT:    i8x16.all_true $push3=, $pop2
-; CHECK-NEXT:    i32.eqz $push4=, $pop3
-; CHECK-NEXT:    return $pop4
+; CHECK-NEXT:    i64.load $push7=, 0($0):p2align=0
+; CHECK-NEXT:    i64.load $push6=, 0($1):p2align=0
+; CHECK-NEXT:    i64.xor $push8=, $pop7, $pop6
+; CHECK-NEXT:    i32.const $push0=, 8
+; CHECK-NEXT:    i32.add $push3=, $0, $pop0
+; CHECK-NEXT:    i64.load $push4=, 0($pop3):p2align=0
+; CHECK-NEXT:    i32.const $push11=, 8
+; CHECK-NEXT:    i32.add $push1=, $1, $pop11
+; CHECK-NEXT:    i64.load $push2=, 0($pop1):p2align=0
+; CHECK-NEXT:    i64.xor $push5=, $pop4, $pop2
+; CHECK-NEXT:    i64.or $push9=, $pop8, $pop5
+; CHECK-NEXT:    i64.eqz $push10=, $pop9
+; CHECK-NEXT:    return $pop10
   %cmp_16 = call i32 @memcmp(ptr %a, ptr %b, i32 16)
   %res = icmp eq i32 %cmp_16, 0
   ret i1 %res