[SystemZ] Do not use glue to represent condition code dependencies

Currently, an instruction setting the condition code is linked to
the instruction using the condition code via a "glue" link in the
SelectionDAG.  This has a number of drawbacks; in particular, it
means the same CC cannot be used by multiple users.  It also makes
it more difficult to efficiently implement SADDO et. al.

This patch changes the back-end to represent CC dependencies as
normal values during SelectionDAG matching, along the lines of
how this is handled in the X86 back-end already.

In addition to the core mechanics of updating all relevant patterns,
this requires a number of additional changes:

- We now need to be able to spill/restore a CC value into a GPR
  if necessary.  This means providing a copyPhysReg implementation
  for moves involving CC, and defining getCrossCopyRegClass.

- Since we still prefer to avoid such spills, we provide an override
  for IsProfitableToFold to avoid creating a merged LOAD / ICMP if
  this would result in multiple users of the CC.

- combineCCMask no longer requires a single CC user, and no longer
  need to be careful about preventing invalid glue/chain cycles.

- emitSelect needs to be more careful in marking CC live-in to
  the basic block it generates.  Also, we can now optimize the
  case of multiple subsequent selects with the same condition
  just like X86 does.

llvm-svn: 331202

1 files changed, 2 insertions, 3 deletions

diff --git a/llvm/test/CodeGen/SystemZ/int-cmp-48.ll b/llvm/test/CodeGen/SystemZ/int-cmp-48.ll
index 821283d19d0..c68a6735764 100644
--- a/llvm/test/CodeGen/SystemZ/int-cmp-48.ll
+++ b/llvm/test/CodeGen/SystemZ/int-cmp-48.ll
@@ -28,9 +28,8 @@ exit:
 ; Check that we do not fold across an aliasing store.
 define void @f2(i8 *%src) {
 ; CHECK-LABEL: f2:
-; CHECK: llc [[REG:%r[0-5]]], 0(%r2)
-; CHECK-DAG: mvi 0(%r2), 0
-; CHECK-DAG: tmll [[REG]], 1
+; CHECK: tm 0(%r2), 1
+; CHECK: mvi 0(%r2), 0
 ; CHECK: ber %r14
 ; CHECK: br %r14
 entry: