From 8df08017d81ef3749acdc3234e3f33c15a6d0def Mon Sep 17 00:00:00 2001
From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Thu, 24 Jun 2010 16:19:28 +0000
Subject: [PATCH] Be more strict about subreg-to-subreg copies in
 CoalescerPair.

Also keep track of the original DstREg before subregister adjustments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106753 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/CodeGen/RegisterCoalescer.h | 16 +++++++++++++++-
 lib/CodeGen/RegisterCoalescer.cpp        | 20 +++++++++++++++-----
 2 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/include/llvm/CodeGen/RegisterCoalescer.h b/include/llvm/CodeGen/RegisterCoalescer.h
index e3d3e796336..7aec10ccb38 100644
--- a/include/llvm/CodeGen/RegisterCoalescer.h
+++ b/include/llvm/CodeGen/RegisterCoalescer.h
@@ -165,9 +165,15 @@ namespace llvm {
     /// virtual register.
     unsigned subIdx_;
 
+    /// origDstReg_ - dstReg_ without subreg adjustments.
+    unsigned origDstReg_;
+
     /// partial_ - True when the original copy was a partial subregister copy.
     bool partial_;
 
+    /// crossClass_ - True when both regs are virtual, and newRC is constrained.
+    bool crossClass_;
+
     /// flipped_ - True when DstReg and SrcReg are reversed from the oriignal copy
     /// instruction.
     bool flipped_;
@@ -186,7 +192,8 @@ namespace llvm {
   public:
     CoalescerPair(const TargetInstrInfo &tii, const TargetRegisterInfo &tri)
       : tii_(tii), tri_(tri), dstReg_(0), srcReg_(0), subIdx_(0),
-        partial_(false), flipped_(false), newRC_(0) {}
+        origDstReg_(0), partial_(false), crossClass_(false), flipped_(false),
+        newRC_(0) {}
 
     /// setRegisters - set registers to match the copy instruction MI. Return
     /// false if MI is not a coalescable copy instruction.
@@ -207,6 +214,9 @@ namespace llvm {
     /// full register, but was a subreg operation.
     bool isPartial() const { return partial_; }
 
+    /// isCrossClass - Return true if DstReg is virtual and NewRC is a smaller register class than DstReg's.
+    bool isCrossClass() const { return crossClass_; }
+
     /// isFlipped - Return true when getSrcReg is the register being defined by
     /// the original copy instruction.
     bool isFlipped() const { return flipped_; }
@@ -222,6 +232,10 @@ namespace llvm {
     /// coalesced into, or 0.
     unsigned getSubIdx() const { return subIdx_; }
 
+    /// getOrigDstReg - Return DstReg as it appeared in the original copy
+    /// instruction before any subreg adjustments.
+    unsigned getOrigDstReg() const { return isPhys() ? origDstReg_ : dstReg_; }
+
     /// getNewRC - Return the register class of the coalesced register.
     const TargetRegisterClass *getNewRC() const { return newRC_; }
   };
diff --git a/lib/CodeGen/RegisterCoalescer.cpp b/lib/CodeGen/RegisterCoalescer.cpp
index b18f0957b62..b943a271b6f 100644
--- a/lib/CodeGen/RegisterCoalescer.cpp
+++ b/lib/CodeGen/RegisterCoalescer.cpp
@@ -63,7 +63,7 @@ bool CoalescerPair::isMoveInstr(const MachineInstr *MI,
 bool CoalescerPair::setRegisters(const MachineInstr *MI) {
   srcReg_ = dstReg_ = subIdx_ = 0;
   newRC_ = 0;
-  flipped_ = false;
+  flipped_ = crossClass_ = false;
 
   unsigned Src, Dst, SrcSub, DstSub;
   if (!isMoveInstr(MI, Src, Dst, SrcSub, DstSub))
@@ -78,6 +78,7 @@ bool CoalescerPair::setRegisters(const MachineInstr *MI) {
     std::swap(SrcSub, DstSub);
     flipped_ = true;
   }
+  origDstReg_ = Dst;
 
   const MachineRegisterInfo &MRI = MI->getParent()->getParent()->getRegInfo();
 
@@ -100,11 +101,19 @@ bool CoalescerPair::setRegisters(const MachineInstr *MI) {
   } else {
     // Both registers are virtual.
 
-    // Identical sub to sub.
-    if (SrcSub == DstSub)
+    // Both registers have subreg indices.
+    if (SrcSub && DstSub) {
+      // For now we only handle the case of identical indices in commensurate
+      // registers: Dreg:ssub_1 + Dreg:ssub_1 -> Dreg
+      // FIXME: Handle Qreg:ssub_3 + Dreg:ssub_1 as QReg:dsub_1 + Dreg.
+      if (SrcSub != DstSub)
+        return false;
+      const TargetRegisterClass *SrcRC = MRI.getRegClass(Src);
+      const TargetRegisterClass *DstRC = MRI.getRegClass(Dst);
+      if (!getCommonSubClass(DstRC, SrcRC))
+        return false;
       SrcSub = DstSub = 0;
-    else if (SrcSub && DstSub)
-      return false; // FIXME: Qreg:ssub_3 + Dreg:ssub_1 => QReg:dsub_1 + Dreg.
+    }
 
     // There can be no SrcSub.
     if (SrcSub) {
@@ -124,6 +133,7 @@ bool CoalescerPair::setRegisters(const MachineInstr *MI) {
       newRC_ = getCommonSubClass(DstRC, SrcRC);
     if (!newRC_)
       return false;
+    crossClass_ = newRC_ != DstRC || newRC_ != SrcRC;
   }
   // Check our invariants
   assert(TargetRegisterInfo::isVirtualRegister(Src) && "Src must be virtual");