[ARM] Do not assume alignment in vld1xN and vst1xN intrinsics (#106984)

These intrinsics currently assume natural alignment. Instead, respect
the alignment attribute on the intrinsic. Teach InstCombine to improve
that alignment.

If desired I could also adjust the clang frontend to add alignment
annotations equivalent to the previous behavior, but I don't see any
indication that such an assumption is correct in the ARM intrinsics
docs.

Fixes #59081.

Author: nikic

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -21073,7 +21073,7 @@ bool ARMTargetLowering::getTgtMemIntrinsic(IntrinsicInfo &Info,
     Info.memVT = EVT::getVectorVT(I.getType()->getContext(), MVT::i64, NumElts);
     Info.ptrVal = I.getArgOperand(I.arg_size() - 1);
     Info.offset = 0;
-    Info.align.reset();
+    Info.align = I.getParamAlign(I.arg_size() - 1).valueOrOne();
     // volatile loads with NEON intrinsics not supported
     Info.flags = MachineMemOperand::MOLoad;
     return true;
@@ -21120,7 +21120,7 @@ bool ARMTargetLowering::getTgtMemIntrinsic(IntrinsicInfo &Info,
     Info.memVT = EVT::getVectorVT(I.getType()->getContext(), MVT::i64, NumElts);
     Info.ptrVal = I.getArgOperand(0);
     Info.offset = 0;
-    Info.align.reset();
+    Info.align = I.getParamAlign(0).valueOrOne();
     // volatile stores with NEON intrinsics not supported
     Info.flags = MachineMemOperand::MOStore;
     return true;

llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp

@@ -163,6 +163,22 @@ ARMTTIImpl::instCombineIntrinsic(InstCombiner &IC, IntrinsicInst &II) const {
     break;
   }
 
+  case Intrinsic::arm_neon_vld1x2:
+  case Intrinsic::arm_neon_vld1x3:
+  case Intrinsic::arm_neon_vld1x4:
+  case Intrinsic::arm_neon_vst1x2:
+  case Intrinsic::arm_neon_vst1x3:
+  case Intrinsic::arm_neon_vst1x4: {
+    Align NewAlign =
+        getKnownAlignment(II.getArgOperand(0), IC.getDataLayout(), &II,
+                          &IC.getAssumptionCache(), &IC.getDominatorTree());
+    Align OldAlign = II.getParamAlign(0).valueOrOne();
+    if (NewAlign > OldAlign)
+      II.addParamAttr(0,
+                      Attribute::getWithAlignment(II.getContext(), NewAlign));
+    break;
+  }
+
   case Intrinsic::arm_mve_pred_i2v: {
     Value *Arg = II.getArgOperand(0);
     Value *ArgArg;