LiveRegUnits: Add accumulateBackward() function

Re-Commit r292543 with a fix for the situation when the chain end is
MBB.end().

This function can be used to accumulate the set of all read and modified
register in a sequence of instructions.

Use this code in AArch64A57FPLoadBalancing::scavengeRegister() to prove
the concept.

- The AArch64A57LoadBalancing code is using a backwards analysis now
  which is irrespective of kill flags. This is the main motivation for
  this change.

Differential Revision: http://reviews.llvm.org/D22082

llvm-svn: 292705

1 files changed, 24 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/LiveRegUnits.cpp b/llvm/lib/CodeGen/LiveRegUnits.cpp
index 14da799a63f..0a10b4e6265 100644
--- a/llvm/lib/CodeGen/LiveRegUnits.cpp
+++ b/llvm/lib/CodeGen/LiveRegUnits.cpp
@@ -26,6 +26,15 @@ void LiveRegUnits::removeRegsNotPreserved(const uint32_t *RegMask) {
   }
 }
 
+void LiveRegUnits::addRegsInMask(const uint32_t *RegMask) {
+  for (unsigned U = 0, E = TRI->getNumRegUnits(); U != E; ++U) {
+    for (MCRegUnitRootIterator RootReg(U, TRI); RootReg.isValid(); ++RootReg) {
+      if (MachineOperand::clobbersPhysReg(RegMask, *RootReg))
+        Units.set(U);
+    }
+  }
+}
+
 void LiveRegUnits::stepBackward(const MachineInstr &MI) {
   // Remove defined registers and regmask kills from the set.
   for (ConstMIBundleOperands O(MI); O.isValid(); ++O) {
@@ -51,6 +60,21 @@ void LiveRegUnits::stepBackward(const MachineInstr &MI) {
   }
 }
 
+void LiveRegUnits::accumulateBackward(const MachineInstr &MI) {
+  // Add defs, uses and regmask clobbers to the set.
+  for (ConstMIBundleOperands O(MI); O.isValid(); ++O) {
+    if (O->isReg()) {
+      unsigned Reg = O->getReg();
+      if (!TargetRegisterInfo::isPhysicalRegister(Reg))
+        continue;
+      if (!O->isDef() && !O->readsReg())
+        continue;
+      addReg(Reg);
+    } else if (O->isRegMask())
+      addRegsInMask(O->getRegMask());
+  }
+}
+
 /// Add live-in registers of basic block \p MBB to \p LiveUnits.
 static void addLiveIns(LiveRegUnits &LiveUnits, const MachineBasicBlock &MBB) {
   for (const auto &LI : MBB.liveins())