================
@@ -21248,6 +21297,51 @@ static SDValue foldTruncStoreOfExt(SelectionDAG &DAG,
SDNode *N) {
return SDValue();
}
+// A custom combine to lower load <3 x i8> as the more efficient sequence
+// below:
+// ldrb wX, [x0, #2]
+// ldrh wY, [x0]
+// orr wX, wY, wX, lsl #16
+// fmov s0, wX
+//
+static SDValue combineV3I8LoadExt(LoadSDNode *LD, SelectionDAG &DAG) {
+ EVT MemVT = LD->getMemoryVT();
+ if (MemVT != EVT::getVectorVT(*DAG.getContext(), MVT::i8, 3) ||
+ LD->getOriginalAlign() >= 4)
+ return SDValue();
+
+ SDLoc DL(LD);
+ MachineFunction &MF = DAG.getMachineFunction();
+ SDValue Chain = LD->getChain();
+ SDValue BasePtr = LD->getBasePtr();
+ MachineMemOperand *MMO = LD->getMemOperand();
+ assert(LD->getOffset().isUndef() && "undef offset expected");
+
+ // Load 2 x i8, then 1 x i8.
+ SDValue L16 = DAG.getLoad(MVT::i16, DL, Chain, BasePtr,
+ MF.getMachineMemOperand(MMO, 0, 2));
+ TypeSize Offset2 = TypeSize::getFixed(2);
+ SDValue L8 = DAG.getLoad(MVT::i8, DL, Chain,
+ DAG.getMemBasePlusOffset(BasePtr, Offset2, DL),
+ MF.getMachineMemOperand(MMO, 2, 1));
+
+ SDValue Ins16 = DAG.getNode(ISD::SPLAT_VECTOR, DL, MVT::v4i16, L16);
+
+ SDValue Cast = DAG.getNode(ISD::BITCAST, DL, MVT::v8i8, Ins16);
+
+ SDValue Ext8 = DAG.getNode(ISD::ZERO_EXTEND, DL, MVT::i32, L8);
+ SDValue Trunc8 = DAG.getNode(ISD::TRUNCATE, DL, MVT::i8, Ext8);
----------------
TNorthover wrote:
What are these two doing? They ought to amount to a nop.
https://github.com/llvm/llvm-project/pull/78632
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