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, 12 insertions, 1 deletions

diff --git a/lib/CodeGen/RegAllocLinearScan.cpp b/lib/CodeGen/RegAllocLinearScan.cpp
index a804e1aa86..e2c1a18b44 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;