From 26bfc08b80c904c71487ac1ab49a8b3a15a8d3e9 Mon Sep 17 00:00:00 2001
From: Alkis Evlogimenos <alkis@evlogimenos.com>
Date: Sun, 28 Dec 2003 17:58:18 +0000
Subject: [PATCH] Add coalescing to register allocator. A hint is added to each
 interval which denotes the register we would like to be assigned to (virtual
 or physical). In register allocation, if this hint exists and we can map it
 to a physical register (it is either a physical register or it is a virtual
 register that already got assigned to a physical one) we use that register if
 it is available instead of a random one in the free pool.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10634 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/CodeGen/LiveIntervalAnalysis.h |  1 +
 include/llvm/CodeGen/LiveIntervals.h        |  1 +
 lib/CodeGen/LiveIntervalAnalysis.cpp        | 18 +++++++++++++++++-
 lib/CodeGen/LiveIntervalAnalysis.h          |  1 +
 lib/CodeGen/RegAllocLinearScan.cpp          | 13 ++++++++++++-
 5 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/include/llvm/CodeGen/LiveIntervalAnalysis.h b/include/llvm/CodeGen/LiveIntervalAnalysis.h
index cecfbbadbdf..8f5fd3a648d 100644
--- a/include/llvm/CodeGen/LiveIntervalAnalysis.h
+++ b/include/llvm/CodeGen/LiveIntervalAnalysis.h
@@ -38,6 +38,7 @@ namespace llvm {
             typedef std::pair<unsigned, unsigned> Range;
             typedef std::vector<Range> Ranges;
             unsigned reg;   // the register of this interval
+            unsigned hint;
             float weight;   // weight of this interval (number of uses
                             // * 10^loopDepth)
             Ranges ranges;  // the ranges this register is valid
diff --git a/include/llvm/CodeGen/LiveIntervals.h b/include/llvm/CodeGen/LiveIntervals.h
index cecfbbadbdf..8f5fd3a648d 100644
--- a/include/llvm/CodeGen/LiveIntervals.h
+++ b/include/llvm/CodeGen/LiveIntervals.h
@@ -38,6 +38,7 @@ namespace llvm {
             typedef std::pair<unsigned, unsigned> Range;
             typedef std::vector<Range> Ranges;
             unsigned reg;   // the register of this interval
+            unsigned hint;
             float weight;   // weight of this interval (number of uses
                             // * 10^loopDepth)
             Ranges ranges;  // the ranges this register is valid
diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index b34a65bc644..4d0916046a0 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -108,6 +108,7 @@ bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
 
     // compute spill weights
     const LoopInfo& loopInfo = getAnalysis<LoopInfo>();
+    const TargetInstrInfo& tii = tm_->getInstrInfo();
 
     for (MbbIndex2MbbMap::iterator
              it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
@@ -130,6 +131,21 @@ bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
                 assert(r2iit != r2iMap_.end());
                 intervals_[r2iit->second].weight += pow(10.0F, loopDepth);
             }
+
+            // add hints for coalescing
+            unsigned src, dst;
+            if (tii.isMoveInstr(*instr, src, dst)) {
+                if (src >= MRegisterInfo::FirstVirtualRegister) {
+                    Reg2IntervalMap::iterator r2iit = r2iMap_.find(src);
+                    assert(r2iit != r2iMap_.end());
+                    intervals_[r2iit->second].hint = dst;
+                }
+                if (dst >= MRegisterInfo::FirstVirtualRegister) {
+                    Reg2IntervalMap::iterator r2iit = r2iMap_.find(dst);
+                    assert(r2iit != r2iMap_.end());
+                    intervals_[r2iit->second].hint = src;
+                }
+            }
         }
     }
 
@@ -329,7 +345,7 @@ void LiveIntervals::computeIntervals()
 }
 
 LiveIntervals::Interval::Interval(unsigned r)
-    : reg(r),
+    : reg(r), hint(0),
       weight((r < MRegisterInfo::FirstVirtualRegister ?
               std::numeric_limits<float>::max() : 0.0F))
 {
diff --git a/lib/CodeGen/LiveIntervalAnalysis.h b/lib/CodeGen/LiveIntervalAnalysis.h
index cecfbbadbdf..8f5fd3a648d 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.h
+++ b/lib/CodeGen/LiveIntervalAnalysis.h
@@ -38,6 +38,7 @@ namespace llvm {
             typedef std::pair<unsigned, unsigned> Range;
             typedef std::vector<Range> Ranges;
             unsigned reg;   // the register of this interval
+            unsigned hint;
             float weight;   // weight of this interval (number of uses
                             // * 10^loopDepth)
             Ranges ranges;  // the ranges this register is valid
diff --git a/lib/CodeGen/RegAllocLinearScan.cpp b/lib/CodeGen/RegAllocLinearScan.cpp
index a804e1aa869..e2c1a18b440 100644
--- a/lib/CodeGen/RegAllocLinearScan.cpp
+++ b/lib/CodeGen/RegAllocLinearScan.cpp
@@ -615,8 +615,19 @@ bool RA::physRegAvailable(unsigned physReg)
 unsigned RA::getFreePhysReg(Intervals::const_iterator cur)
 {
     DEBUG(std::cerr << "\t\tgetting free physical register: ");
-
     const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
+
+    if (unsigned reg = cur->hint) {
+        if (reg >= MRegisterInfo::FirstVirtualRegister &&
+            v2pMap_.find(reg) != v2pMap_.end())
+            reg = v2pMap_[reg];
+        if (reg && reg < MRegisterInfo::FirstVirtualRegister &&
+            mri_->getRegClass(reg) == rc && !regUse_[reg]) {
+            DEBUG(std::cerr << mri_->getName(reg) << '\n');
+            return reg;
+        }
+    }
+            
     for (TargetRegisterClass::iterator i = rc->allocation_order_begin(*mf_);
          i != rc->allocation_order_end(*mf_); ++i) {
         unsigned reg = *i;