Allow the register scavenger to spill multiple registers

This patch lets the register scavenger make use of multiple spill slots in
order to guarantee that it will be able to provide multiple registers
simultaneously.

To support this, the RS's API has changed slightly: setScavengingFrameIndex /
getScavengingFrameIndex have been replaced by addScavengingFrameIndex /
isScavengingFrameIndex / getScavengingFrameIndices.

In forthcoming commits, the PowerPC backend will use this capability in order
to implement the spilling of condition registers, and some special-purpose
registers, without relying on r0 being reserved. In some cases, spilling these
registers requires two GPRs: one for addressing and one to hold the value being
transferred.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177774 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 37 insertions, 15 deletions

diff --git a/include/llvm/CodeGen/RegisterScavenging.h b/include/llvm/CodeGen/RegisterScavenging.h
index a2b1533e5d..babb96b962 100644
--- a/include/llvm/CodeGen/RegisterScavenging.h
+++ b/include/llvm/CodeGen/RegisterScavenging.h
@@ -40,17 +40,23 @@ class RegScavenger {
   /// registers.
   bool Tracking;
 
-  /// ScavengingFrameIndex - Special spill slot used for scavenging a register
-  /// post register allocation.
-  int ScavengingFrameIndex;
+  /// Information on scavenged registers (held in a spill slot).
+  struct ScavengedInfo {
+    ScavengedInfo(int FI) : FrameIndex(FI), Reg(0), Restore(NULL) {}
 
-  /// ScavengedReg - If none zero, the specific register is currently being
-  /// scavenged. That is, it is spilled to the special scavenging stack slot.
-  unsigned ScavengedReg;
+    /// A spill slot used for scavenging a register post register allocation.
+    int FrameIndex;
 
-  /// ScavengeRestore - Instruction that restores the scavenged register from
-  /// stack.
-  const MachineInstr *ScavengeRestore;
+    /// If non-zero, the specific register is currently being
+    /// scavenged. That is, it is spilled to this scavenging stack slot.
+    unsigned Reg;
+
+    /// The instruction that restores the scavenged register from stack.
+    const MachineInstr *Restore;
+  };
+
+  /// A vector of information on scavenged registers.
+  SmallVector<ScavengedInfo, 2> Scavenged;
 
   /// CalleeSavedrRegs - A bitvector of callee saved registers for the target.
   ///
@@ -67,8 +73,7 @@ class RegScavenger {
 
 public:
   RegScavenger()
-    : MBB(NULL), NumPhysRegs(0), Tracking(false),
-      ScavengingFrameIndex(-1), ScavengedReg(0) {}
+    : MBB(NULL), NumPhysRegs(0), Tracking(false) {}
 
   /// enterBasicBlock - Start tracking liveness from the begin of the specific
   /// basic block.
@@ -103,10 +108,27 @@ public:
   /// Return 0 if none is found.
   unsigned FindUnusedReg(const TargetRegisterClass *RegClass) const;
 
-  /// setScavengingFrameIndex / getScavengingFrameIndex - accessor and setter of
-  /// ScavengingFrameIndex.
-  void setScavengingFrameIndex(int FI) { ScavengingFrameIndex = FI; }
-  int getScavengingFrameIndex() const { return ScavengingFrameIndex; }
+  /// Add a scavenging frame index.
+  void addScavengingFrameIndex(int FI) {
+    Scavenged.push_back(ScavengedInfo(FI));
+  }
+
+  /// Query whether a frame index is a scavenging frame index.
+  bool isScavengingFrameIndex(int FI) const {
+    for (SmallVector<ScavengedInfo, 2>::const_iterator I = Scavenged.begin(),
+         IE = Scavenged.end(); I != IE; ++I)
+      if (I->FrameIndex == FI)
+        return true;
+
+    return false;
+  }
+
+  /// Get an array of scavenging frame indices.
+  void getScavengingFrameIndices(SmallVectorImpl<int> &A) const {
+    for (SmallVector<ScavengedInfo, 2>::const_iterator I = Scavenged.begin(),
+         IE = Scavenged.end(); I != IE; ++I)
+      A.push_back(I->FrameIndex);
+  }
 
   /// scavengeRegister - Make a register of the specific register class
   /// available and do the appropriate bookkeeping. SPAdj is the stack