[SystemZ] implement shouldCoalesce()

Implement shouldCoalesce() to help regalloc avoid running out of GR128
registers.

If a COPY involving a subreg of a GR128 is coalesced, the live range of the
GR128 virtual register will be extended. If this happens where there are
enough phys-reg clobbers present, regalloc will run out of registers (if
there is not a single GR128 allocatable register available).

This patch tries to allow coalescing only when it can prove that this will be
safe by checking the (local) interval in question.

Review: Ulrich Weigand, Quentin Colombet
https://reviews.llvm.org/D37899
https://bugs.llvm.org/show_bug.cgi?id=34610

llvm-svn: 314516

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/RegisterCoalescer.cpp b/llvm/lib/CodeGen/RegisterCoalescer.cpp
index 255d17078a1..152149ac9a7 100644
--- a/llvm/lib/CodeGen/RegisterCoalescer.cpp
+++ b/llvm/lib/CodeGen/RegisterCoalescer.cpp
@@ -1583,7 +1583,7 @@ bool RegisterCoalescer::joinCopy(MachineInstr *CopyMI, bool &Again) {
       std::swap(SrcRC, DstRC);
     }
     if (!TRI->shouldCoalesce(CopyMI, SrcRC, SrcIdx, DstRC, DstIdx,
-                            CP.getNewRC())) {
+                             CP.getNewRC(), *LIS)) {
       DEBUG(dbgs() << "\tSubtarget bailed on coalescing.\n");
       return false;
     }