Lower GT_INDEX into "(base + elemOffsetCns) + index" on arm arch

src/coreclr/jit/morph.cpp

@@ -4909,7 +4909,7 @@ void Compiler::fgMakeOutgoingStructArgCopy(GenTreeCall* call,
  GenTree* arg = fgMakeTmpArgNode(argEntry);
 
  // Change the expression to "(tmp=val),tmp"
- arg  = gtNewOperNode(GT_COMMA, arg->TypeGet(), copyBlk, arg);
+ arg = gtNewOperNode(GT_COMMA, arg->TypeGet(), copyBlk, arg);
 
 #endif // FEATURE_FIXED_OUT_ARGS
 
@@ -5465,11 +5465,23 @@ GenTree* Compiler::fgMorphArrayIndex(GenTree* tree)
 
  GenTree* cns = gtNewIconNode(elemOffs, TYP_I_IMPL);
 
+#ifdef TARGET_ARMARCH
+ // For ARM/ARM64 we create the following tree:
+ //
+ // (arrRef + elemOffset) + (index)
+ //
+ // instead of this for xarch:
+ //
+ // arrRef + (index + elemOffset)
+ //
+ // It allows us to hoist '(arrRef + elemOffset)' part in loops while on XArch
+ // it will be handled via more powerful addressing modes.
+ GenTree* basePlusOffset = gtNewOperNode(GT_ADD, TYP_BYREF, arrRef, cns);
+ addr = gtNewOperNode(GT_ADD, TYP_BYREF, basePlusOffset, addr);
+#else
  addr = gtNewOperNode(GT_ADD, TYP_I_IMPL, addr, cns);
-
- /* Add the object ref to the element's offset */
-
  addr = gtNewOperNode(GT_ADD, TYP_BYREF, arrRef, addr);
+#endif
 
  assert(((tree->gtDebugFlags & GTF_DEBUG_NODE_LARGE) != 0) ||
  (GenTree::s_gtNodeSizes[GT_IND] == TREE_NODE_SZ_SMALL));
@@ -5539,16 +5551,16 @@ GenTree* Compiler::fgMorphArrayIndex(GenTree* tree)
  tree = gtNewOperNode(GT_COMMA, tree->TypeGet(), arrRefDefn, tree);
  }
 
- JITDUMP("fgMorphArrayIndex (before remorph):\n");
- DISPTREE(tree);
+ JITDUMP("fgMorphArrayIndex (before remorph):\n")
+ DISPTREE(tree)
 
  // Currently we morph the tree to perform some folding operations prior
  // to attaching fieldSeq info and labeling constant array index contributions
  //
  tree = fgMorphTree(tree);
 
- JITDUMP("fgMorphArrayIndex (after remorph):\n");
- DISPTREE(tree);
+ JITDUMP("fgMorphArrayIndex (after remorph):\n")
+ DISPTREE(tree)
 
  // Ideally we just want to proceed to attaching fieldSeq info and labeling the
  // constant array index contributions, but the morphing operation may have changed
@@ -5572,38 +5584,51 @@ GenTree* Compiler::fgMorphArrayIndex(GenTree* tree)
  assert(!fgGlobalMorph || (arrElem->gtDebugFlags & GTF_DEBUG_NODE_MORPHED));
  DBEXEC(fgGlobalMorph && (arrElem == tree), tree->gtDebugFlags &= ~GTF_DEBUG_NODE_MORPHED);
 
- addr = arrElem->AsOp()->gtOp1;
+ addr = arrElem->gtGetOp1();
 
- assert(addr->TypeGet() == TYP_BYREF);
+ assert(addr->TypeIs(TYP_BYREF));
 
  GenTree* cnsOff = nullptr;
- if (addr->OperGet() == GT_ADD)
+ if (addr->OperIs(GT_ADD))
  {
- assert(addr->TypeGet() == TYP_BYREF);
- assert(addr->AsOp()->gtOp1->TypeGet() == TYP_REF);
-
- addr = addr->AsOp()->gtOp2;
+#ifdef TARGET_ARMARCH
+ // On arm/arm64 addr tree is a bit different, see above ^
+ if (addr->gtGetOp1()->OperIs(GT_ADD) && addr->gtGetOp1()->gtGetOp2()->IsCnsIntOrI())
+ {
+ assert(addr->gtGetOp1()->gtGetOp1()->TypeIs(TYP_REF));
+ cnsOff = addr->gtGetOp1()->gtGetOp2();
+ addr = addr->gtGetOp2();
+ // Label any constant array index contributions with #ConstantIndex and any LclVars with GTF_VAR_ARR_INDEX
+ addr->LabelIndex(this);
+ }
+ else if (addr->gtGetOp2()->IsCnsIntOrI())
+ {
+ cnsOff = addr->gtGetOp2();
+ addr = nullptr;
+ }
+#else
+ assert(addr->gtGetOp1()->TypeIs(TYP_REF));
+ addr = addr->gtGetOp2();
 
  // Look for the constant [#FirstElem] node here, or as the RHS of an ADD.
-
- if (addr->gtOper == GT_CNS_INT)
+ if (addr->IsCnsIntOrI())
  {
  cnsOff = addr;
  addr = nullptr;
  }
  else
  {
- if ((addr->OperGet() == GT_ADD) && (addr->AsOp()->gtOp2->gtOper == GT_CNS_INT))
+ if ((addr->OperIs(GT_ADD)) && addr->gtGetOp2()->IsCnsIntOrI())
  {
- cnsOff = addr->AsOp()->gtOp2;
- addr = addr->AsOp()->gtOp1;
+ cnsOff = addr->gtGetOp2();
+ addr = addr->gtGetOp1();
  }
-
  // Label any constant array index contributions with #ConstantIndex and any LclVars with GTF_VAR_ARR_INDEX
  addr->LabelIndex(this);
  }
+#endif
  }
- else if (addr->OperGet() == GT_CNS_INT)
+ else if (addr->IsCnsIntOrI())
  {
  cnsOff = addr;
  }