[AAarch64] Optimize CSINC-branch sequence

Peephole optimization that generates a single conditional branch
for csinc-branch sequences like in the examples below. This is
possible when the csinc sets or clears a register based on a condition
code and the branch checks that register. Also the condition
code may not be modified between the csinc and the original branch.

Examples:

1. Convert csinc w9, wzr, wzr, <CC>;tbnz w9, #0, 0x44
   to b.<invCC>

2. Convert csinc w9, wzr, wzr, <CC>; tbz w9, #0, 0x44
   to b.<CC>


rdar://problem/18506500

llvm-svn: 219742

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/PeepholeOptimizer.cpp b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
index 7c195a89bd7..90a4dcf8243 100644
--- a/llvm/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
@@ -135,6 +135,7 @@ namespace {
     bool optimizeExtInstr(MachineInstr *MI, MachineBasicBlock *MBB,
                           SmallPtrSetImpl<MachineInstr*> &LocalMIs);
     bool optimizeSelect(MachineInstr *MI);
+    bool optimizeCondBranch(MachineInstr *MI);
     bool optimizeCopyOrBitcast(MachineInstr *MI);
     bool optimizeCoalescableCopy(MachineInstr *MI);
     bool optimizeUncoalescableCopy(MachineInstr *MI,
@@ -498,6 +499,12 @@ bool PeepholeOptimizer::optimizeSelect(MachineInstr *MI) {
   return true;
 }
 
+/// \brief Check if a simpler conditional branch can be
+// generated
+bool PeepholeOptimizer::optimizeCondBranch(MachineInstr *MI) {
+  return TII->optimizeCondBranch(MI);
+}
+
 /// \brief Check if the registers defined by the pair (RegisterClass, SubReg)
 /// share the same register file.
 static bool shareSameRegisterFile(const TargetRegisterInfo &TRI,
@@ -1104,6 +1111,11 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &mf) {
         continue;
       }
 
+      if (MI->isConditionalBranch() && optimizeCondBranch(MI)) {
+        Changed = true;
+        continue;
+      }
+
       if (isCoalescableCopy(*MI) && optimizeCoalescableCopy(MI)) {
         // MI is just rewritten.
         Changed = true;