Do not mark op2 as delayRegFree if op1==op2 (#53964)

* Do not mark op2 as delayRegFree if op1==op2

* Revert NodesAreEquivalentLeaves change

* Pass rmwNode to `BuildDelayFreeUses()` which does the right thing

* Make similar change in arm64

* remove TODO comment

* review feedback

1 files changed, 12 insertions, 48 deletions

diff --git a/src/coreclr/jit/lsraarm64.cpp b/src/coreclr/jit/lsraarm64.cpp
index 223dc906bad..a7a14fdfe54 100644
--- a/src/coreclr/jit/lsraarm64.cpp
+++ b/src/coreclr/jit/lsraarm64.cpp
@@ -1112,54 +1112,11 @@ int LinearScan::BuildHWIntrinsic(GenTreeHWIntrinsic* intrinsicTree)
             // RMW intrinsic operands doesn't have to be delayFree when they can be assigned the same register as op1Reg
             // (i.e. a register that corresponds to read-modify-write operand) and one of them is the last use.
 
-            bool op2DelayFree = isRMW;
-            bool op3DelayFree = isRMW;
-            bool op4DelayFree = isRMW;
-
             assert(intrin.op1 != nullptr);
 
-            if (isRMW && intrin.op1->OperIs(GT_LCL_VAR))
-            {
-                unsigned int varNum1    = intrin.op1->AsLclVar()->GetLclNum();
-                bool         op1LastUse = false;
-
-                unsigned int varNum2 = BAD_VAR_NUM;
-                unsigned int varNum3 = BAD_VAR_NUM;
-                unsigned int varNum4 = BAD_VAR_NUM;
-
-                if (intrin.op2->OperIs(GT_LCL_VAR))
-                {
-                    varNum2 = intrin.op2->AsLclVar()->GetLclNum();
-                    op1LastUse |= ((varNum1 == varNum2) && intrin.op2->HasLastUse());
-                }
-
-                if (intrin.op3 != nullptr)
-                {
-                    if (intrin.op3->OperIs(GT_LCL_VAR))
-                    {
-                        varNum3 = intrin.op3->AsLclVar()->GetLclNum();
-                        op1LastUse |= ((varNum1 == varNum3) && intrin.op3->HasLastUse());
-                    }
-
-                    if ((intrin.op4 != nullptr) && intrin.op4->OperIs(GT_LCL_VAR))
-                    {
-                        varNum4 = intrin.op4->AsLclVar()->GetLclNum();
-                        op1LastUse |= ((varNum1 == varNum4) && intrin.op4->HasLastUse());
-                    }
-                }
-
-                if (op1LastUse)
-                {
-                    op2DelayFree = (varNum1 != varNum2);
-                    op3DelayFree = (varNum1 != varNum3);
-                    op4DelayFree = (varNum1 != varNum4);
-                }
-            }
-
+            bool forceOp2DelayFree = false;
             if ((intrin.id == NI_Vector64_GetElement) || (intrin.id == NI_Vector128_GetElement))
             {
-                assert(!op2DelayFree);
-
                 if (!intrin.op2->IsCnsIntOrI() && (!intrin.op1->isContained() || intrin.op1->OperIsLocal()))
                 {
                     // If the index is not a constant and the object is not contained or is a local
@@ -1168,7 +1125,7 @@ int LinearScan::BuildHWIntrinsic(GenTreeHWIntrinsic* intrinsicTree)
                     // TODO-Cleanup: An internal register will never clobber a source; this code actually
                     // ensures that the index (op2) doesn't interfere with the target.
                     buildInternalIntRegisterDefForNode(intrinsicTree);
-                    op2DelayFree = true;
+                    forceOp2DelayFree = true;
                 }
 
                 if (!intrin.op2->IsCnsIntOrI() && !intrin.op1->isContained())
@@ -1179,15 +1136,22 @@ int LinearScan::BuildHWIntrinsic(GenTreeHWIntrinsic* intrinsicTree)
                 }
             }
 
-            srcCount += op2DelayFree ? BuildDelayFreeUses(intrin.op2) : BuildOperandUses(intrin.op2);
+            if (forceOp2DelayFree)
+            {
+                srcCount += BuildDelayFreeUses(intrin.op2);
+            }
+            else
+            {
+                srcCount += isRMW ? BuildDelayFreeUses(intrin.op2, intrin.op1) : BuildOperandUses(intrin.op2);
+            }
 
             if (intrin.op3 != nullptr)
             {
-                srcCount += op3DelayFree ? BuildDelayFreeUses(intrin.op3) : BuildOperandUses(intrin.op3);
+                srcCount += isRMW ? BuildDelayFreeUses(intrin.op3, intrin.op1) : BuildOperandUses(intrin.op3);
 
                 if (intrin.op4 != nullptr)
                 {
-                    srcCount += op4DelayFree ? BuildDelayFreeUses(intrin.op4) : BuildOperandUses(intrin.op4);
+                    srcCount += isRMW ? BuildDelayFreeUses(intrin.op4, intrin.op1) : BuildOperandUses(intrin.op4);
                 }
             }
         }