[RISCV] add load/store misched/PostRA cluster options

Some processors benefit more from store clustering than load clustering,
and vice-versa, depending on factors that are exclusive to each one
(e.g. macrofusions implemented).

Likewise, certain optimizations benefits more from misched clustering
than postRA clustering. Macrofusions are again an example: in a
processor with store pair macrofusions, like the veyron-v1, it is
observed that misched clustering increases the amount of macrofusions
more than postRA clustering.  This of course isn't necessarily true for
other processors, but it shows that processors can benefit from a more
fine grained control of clustering mutations, and each one is able to do
it differently.

Add 4 new clustering options to be used with the existing
riscv-misched-load-store-clustering and
riscv-postmisched-load-store-clustering:

- riscv-misched-load-clustering and riscv-misched-store-clustering:
  enable/disable load/store clustering during misched;

- riscv-postmisched-load-clustering and
  riscv-postmisched-store-clustering: enable/disable load/store
  clustering during PostRA.

To preserve the existing behavior of the existing flags all options added
are default 'true'. Note that the two existing flags have precedence, so
setting "riscv-misched-load-store-clustering=false" will disable load
mutations even if setting riscv-misched-load-clustering=true. Same thing
with stores and with the postRA options.

For the veyron-v1 case mentioned above, to enable just the store clustering
during misched, offline everything else:

-mllvm -riscv-misched-load-clustering=false -mllvm -riscv-postmisched-load-store-clustering=false

Author: danielhb

llvm/lib/Target/RISCV/RISCVTargetMachine.cpp

@@ -99,11 +99,31 @@ static cl::opt<bool> EnableMISchedLoadStoreClustering(
     cl::desc("Enable load and store clustering in the machine scheduler"),
     cl::init(true));
 
+static cl::opt<bool> EnableMISchedLoadClustering(
+    "riscv-misched-load-clustering", cl::Hidden,
+    cl::desc("Enable load clustering in the machine scheduler"),
+    cl::init(true));
+
+static cl::opt<bool> EnableMISchedStoreClustering(
+    "riscv-misched-store-clustering", cl::Hidden,
+    cl::desc("Enable store clustering in the machine scheduler"),
+    cl::init(true));
+
 static cl::opt<bool> EnablePostMISchedLoadStoreClustering(
     "riscv-postmisched-load-store-clustering", cl::Hidden,
     cl::desc("Enable PostRA load and store clustering in the machine scheduler"),
     cl::init(true));
 
+static cl::opt<bool> EnablePostMISchedLoadClustering(
+    "riscv-postmisched-load-clustering", cl::Hidden,
+    cl::desc("Enable PostRA load clustering in the machine scheduler"),
+    cl::init(true));
+
+static cl::opt<bool> EnablePostMISchedStoreClustering(
+    "riscv-postmisched-store-clustering", cl::Hidden,
+    cl::desc("Enable PostRA store clustering in the machine scheduler"),
+    cl::init(true));
+
 static cl::opt<bool>
     EnableVLOptimizer("riscv-enable-vl-optimizer",
                       cl::desc("Enable the RISC-V VL Optimizer pass"),
@@ -301,10 +321,13 @@ ScheduleDAGInstrs *
 RISCVTargetMachine::createMachineScheduler(MachineSchedContext *C) const {
   ScheduleDAGMILive *DAG = createSchedLive(C);
   if (EnableMISchedLoadStoreClustering) {
-    DAG->addMutation(createLoadClusterDAGMutation(
-        DAG->TII, DAG->TRI, /*ReorderWhileClustering=*/true));
-    DAG->addMutation(createStoreClusterDAGMutation(
-        DAG->TII, DAG->TRI, /*ReorderWhileClustering=*/true));
+    if (EnableMISchedLoadClustering)
+      DAG->addMutation(createLoadClusterDAGMutation(
+          DAG->TII, DAG->TRI, /*ReorderWhileClustering=*/true));
+
+    if (EnableMISchedStoreClustering)
+      DAG->addMutation(createStoreClusterDAGMutation(
+          DAG->TII, DAG->TRI, /*ReorderWhileClustering=*/true));
   }
 
   const RISCVSubtarget &ST = C->MF->getSubtarget<RISCVSubtarget>();
@@ -318,10 +341,13 @@ ScheduleDAGInstrs *
 RISCVTargetMachine::createPostMachineScheduler(MachineSchedContext *C) const {
   ScheduleDAGMI *DAG = createSchedPostRA(C);
   if (EnablePostMISchedLoadStoreClustering) {
-    DAG->addMutation(createLoadClusterDAGMutation(
-        DAG->TII, DAG->TRI, /*ReorderWhileClustering=*/true));
-    DAG->addMutation(createStoreClusterDAGMutation(
-        DAG->TII, DAG->TRI, /*ReorderWhileClustering=*/true));
+    if (EnablePostMISchedLoadClustering)
+      DAG->addMutation(createLoadClusterDAGMutation(
+          DAG->TII, DAG->TRI, /*ReorderWhileClustering=*/true));
+
+    if (EnablePostMISchedStoreClustering)
+      DAG->addMutation(createStoreClusterDAGMutation(
+          DAG->TII, DAG->TRI, /*ReorderWhileClustering=*/true));
   }
 
   return DAG;