misched: DAG builder support for tracking register pressure within the current scheduling region.

The DAG builder is a convenient place to do it. Hopefully this is more
efficient than a separate traversal over the same region.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155456 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/ScheduleDAGInstrs.cpp

@@ -13,6 +13,7 @@
 //===----------------------------------------------------------------------===//
 
 #define DEBUG_TYPE "sched-instrs"
+#include "RegisterPressure.h"
 #include "llvm/Operator.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/ValueTracking.h"
@@ -504,7 +505,11 @@ void ScheduleDAGInstrs::initSUnits() {
   }
 }
 
-void ScheduleDAGInstrs::buildSchedGraph(AliasAnalysis *AA) {
+/// If RegPressure is non null, compute register pressure as a side effect. The
+/// DAG builder is an efficient place to do it because it already visits
+/// operands.
+void ScheduleDAGInstrs::buildSchedGraph(AliasAnalysis *AA,
+                                        RegPressureTracker *RPTracker) {
   // Create an SUnit for each real instruction.
   initSUnits();
 
@@ -555,6 +560,10 @@ void ScheduleDAGInstrs::buildSchedGraph(AliasAnalysis *AA) {
       PrevMI = MI;
       continue;
     }
+    if (RPTracker) {
+      RPTracker->recede();
+      assert(RPTracker->getPos() == prior(MII) && "RPTracker can't find MI");
+    }
 
     assert((!MI->isTerminator() || CanHandleTerminators) && !MI->isLabel() &&
            "Cannot schedule terminators or labels!");