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

1 files changed, 17 insertions, 1 deletions

diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index b34a65bc64..4d0916046a 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))
 {