Spill multiple registers at once.

Live range splitting can create a number of small live ranges containing only a
single real use. Spill these small live ranges along with the large range they
are connected to with copies. This enables memory operand folding and maximizes
the spill to fill distance.

Work in progress with known bugs.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127529 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 0 deletions

diff --git a/lib/CodeGen/RegAllocBasic.cpp b/lib/CodeGen/RegAllocBasic.cpp
index 9df2047a66..d51be52027 100644
--- a/lib/CodeGen/RegAllocBasic.cpp
+++ b/lib/CodeGen/RegAllocBasic.cpp
@@ -289,6 +289,13 @@ void RegAllocBase::allocatePhysRegs() {
 
   // Continue assigning vregs one at a time to available physical registers.
   while (LiveInterval *VirtReg = dequeue()) {
+    // Unused registers can appear when the spiller coalesces snippets.
+    if (MRI->reg_nodbg_empty(VirtReg->reg)) {
+      DEBUG(dbgs() << "Dropping unused " << *VirtReg << '\n');
+      LIS->removeInterval(VirtReg->reg);
+      continue;
+    }
+
     // selectOrSplit requests the allocator to return an available physical
     // register if possible and populate a list of new live intervals that
     // result from splitting.