[PowerPC] Remove redundant CRSET/CRUNSET in custom lowering of known CR bit spills

We lower known CR bit spills (CRSET/CRUNSET) to load and spill the known value
but forgot to remove the redundant spills.

e.g., This sequence was used to spill a CRUNSET:
    crclr   4*cr5+lt
    mfocrf  r3,4
    rlwinm  r3,r3,20,0,0
    stw     r3,132(r1)

Custom lowering of known CR bit spills lower it to:
    crxor 4*cr5+lt, 4*cr5+lt, 4*cr5+lt
    li  r3,0
    stw r3,132(r1)

crxor is redundant if there is no use of 4*cr5+lt so we should remove it

Differential revision: https://reviews.llvm.org/D67722

1 files changed, 16 insertions, 1 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCPreEmitPeephole.cpp b/llvm/lib/Target/PowerPC/PPCPreEmitPeephole.cpp
index 15c09a5a868..a4b4bf2973d 100644
--- a/llvm/lib/Target/PowerPC/PPCPreEmitPeephole.cpp
+++ b/llvm/lib/Target/PowerPC/PPCPreEmitPeephole.cpp
@@ -163,8 +163,19 @@ namespace {
     }
 
     bool runOnMachineFunction(MachineFunction &MF) override {
-      if (skipFunction(MF.getFunction()) || !RunPreEmitPeephole)
+      if (skipFunction(MF.getFunction()) || !RunPreEmitPeephole) {
+        // Remove UNENCODED_NOP even when this pass is disabled.
+        // This needs to be done unconditionally so we don't emit zeros
+        // in the instruction stream.
+        SmallVector<MachineInstr *, 4> InstrsToErase;
+        for (MachineBasicBlock &MBB : MF)
+          for (MachineInstr &MI : MBB)
+            if (MI.getOpcode() == PPC::UNENCODED_NOP)
+              InstrsToErase.push_back(&MI);
+        for (MachineInstr *MI : InstrsToErase)
+          MI->eraseFromParent();
         return false;
+      }
       bool Changed = false;
       const PPCInstrInfo *TII = MF.getSubtarget<PPCSubtarget>().getInstrInfo();
       const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
@@ -173,6 +184,10 @@ namespace {
         Changed |= removeRedundantLIs(MBB, TRI);
         for (MachineInstr &MI : MBB) {
           unsigned Opc = MI.getOpcode();
+          if (Opc == PPC::UNENCODED_NOP) {
+            InstrsToErase.push_back(&MI);
+            continue;
+          }
           // Detect self copies - these can result from running AADB.
           if (PPCInstrInfo::isSameClassPhysRegCopy(Opc)) {
             const MCInstrDesc &MCID = TII->get(Opc);