gpu-compute: Check for WAX dependences

This adds checking if the destination registers are free or busy
in the operandsReady() function for both scalar and vector
registers. This allows us to catch WAX dependences between instructions.

Change-Id: I0fb0b29e9608fca0d90c059422d4d9500d5b2a7d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/47539
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/gpu-compute/scalar_register_file.cc

@@ -64,6 +64,17 @@ ScalarRegisterFile::operandsReady(Wavefront *w, GPUDynInstPtr ii) const
         }
     }
 
+    for (const auto& dstScalarOp : ii->dstScalarRegOperands()) {
+        for (const auto& physIdx : dstScalarOp.physIndices()) {
+            if (regBusy(physIdx)) {
+                DPRINTF(GPUSRF, "WAX stall: WV[%d]: %s: physReg[%d]\n",
+                        w->wfDynId, ii->disassemble(), physIdx);
+                w->stats.numTimesBlockedDueWAXDependencies++;
+                return false;
+            }
+        }
+    }
+
     return true;
 }
 

src/gpu-compute/vector_register_file.cc

@@ -71,6 +71,17 @@ VectorRegisterFile::operandsReady(Wavefront *w, GPUDynInstPtr ii) const
         }
     }
 
+    for (const auto& dstVecOp : ii->dstVecRegOperands()) {
+        for (const auto& physIdx : dstVecOp.physIndices()) {
+            if (regBusy(physIdx)) {
+                DPRINTF(GPUVRF, "WAX stall: WV[%d]: %s: physReg[%d]\n",
+                        w->wfDynId, ii->disassemble(), physIdx);
+                w->stats.numTimesBlockedDueWAXDependencies++;
+                return false;
+            }
+        }
+    }
+
     return true;
 }