cpu: remove unnecessary data ptr from O3 internal read() funcs

The read() function merely initiates a memory read operation; the
data doesn't arrive until the access completes and a response packet
is received from the memory system.  Thus there's no need to provide
a data pointer; its existence is historical.

Getting this pointer out of this internal o3 interface sets the
stage for similar cleanup in the ExecContext interface.  Also
found that we were pointlessly setting the contents at this pointer
on a store forward (the useful memcpy happens just a few lines
below the deleted one).

src/cpu/base_dyn_inst.hh

@@ -910,7 +910,7 @@ BaseDynInst<Impl>::readMem(Addr addr, uint8_t *data,
                 }
                 reqToVerify = new Request(*req);
             }
-            fault = cpu->read(req, sreqLow, sreqHigh, data, lqIdx);
+            fault = cpu->read(req, sreqLow, sreqHigh, lqIdx);
         } else {
             // Commit will have to clean up whatever happened.  Set this
             // instruction as executed.

src/cpu/o3/cpu.hh

@@ -678,10 +678,9 @@ class FullO3CPU : public BaseO3CPU
 
     /** CPU read function, forwards read to LSQ. */
     Fault read(RequestPtr &req, RequestPtr &sreqLow, RequestPtr &sreqHigh,
-               uint8_t *data, int load_idx)
+               int load_idx)
     {
-        return this->iew.ldstQueue.read(req, sreqLow, sreqHigh,
-                                        data, load_idx);
+        return this->iew.ldstQueue.read(req, sreqLow, sreqHigh, load_idx);
     }
 
     /** CPU write function, forwards write to LSQ. */

src/cpu/o3/lsq.hh

@@ -275,7 +275,7 @@ class LSQ {
      * index.
      */
     Fault read(RequestPtr req, RequestPtr sreqLow, RequestPtr sreqHigh,
-               uint8_t *data, int load_idx);
+               int load_idx);
 
     /** Executes a store operation, using the store specified at the store
      * index.
@@ -332,11 +332,11 @@ class LSQ {
 template <class Impl>
 Fault
 LSQ<Impl>::read(RequestPtr req, RequestPtr sreqLow, RequestPtr sreqHigh,
-                uint8_t *data, int load_idx)
+                int load_idx)
 {
     ThreadID tid = req->threadId();
 
-    return thread[tid].read(req, sreqLow, sreqHigh, data, load_idx);
+    return thread[tid].read(req, sreqLow, sreqHigh, load_idx);
 }
 
 template <class Impl>

src/cpu/o3/lsq_unit.hh

@@ -511,7 +511,7 @@ class LSQUnit {
   public:
     /** Executes the load at the given index. */
     Fault read(Request *req, Request *sreqLow, Request *sreqHigh,
-               uint8_t *data, int load_idx);
+               int load_idx);
 
     /** Executes the store at the given index. */
     Fault write(Request *req, Request *sreqLow, Request *sreqHigh,
@@ -550,7 +550,7 @@ class LSQUnit {
 template <class Impl>
 Fault
 LSQUnit<Impl>::read(Request *req, Request *sreqLow, Request *sreqHigh,
-                    uint8_t *data, int load_idx)
+                    int load_idx)
 {
     DynInstPtr load_inst = loadQueue[load_idx];
 
@@ -676,12 +676,6 @@ LSQUnit<Impl>::read(Request *req, Request *sreqLow, Request *sreqHigh,
             // Get shift amount for offset into the store's data.
             int shift_amt = req->getVaddr() - storeQueue[store_idx].inst->effAddr;
 
-            if (storeQueue[store_idx].isAllZeros)
-                memset(data, 0, req->getSize());
-            else
-                memcpy(data, storeQueue[store_idx].data + shift_amt,
-                   req->getSize());
-
             // Allocate memory if this is the first time a load is issued.
             if (!load_inst->memData) {
                 load_inst->memData = new uint8_t[req->getSize()];