Add an MCID::Select flag and TII hooks for optimizing selects.

Select instructions pick one of two virtual registers based on a
condition, like x86 cmov. On targets like ARM that support predication,
selects can sometimes be eliminated by predicating the instruction
defining one of the operands.

Teach PeepholeOptimizer to recognize select instructions, and ask the
target to optimize them.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162059 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 0 deletions

diff --git a/include/llvm/MC/MCInstrDesc.h b/include/llvm/MC/MCInstrDesc.h
index 186612d904..dbf16d8700 100644
--- a/include/llvm/MC/MCInstrDesc.h
+++ b/include/llvm/MC/MCInstrDesc.h
@@ -107,6 +107,7 @@ namespace MCID {
     Compare,
     MoveImm,
     Bitcast,
+    Select,
     DelaySlot,
     FoldableAsLoad,
     MayLoad,
@@ -282,6 +283,12 @@ public:
     return Flags & (1 << MCID::Bitcast);
   }
 
+  /// isSelect - Return true if this is a select instruction.
+  ///
+  bool isSelect() const {
+    return Flags & (1 << MCID::Select);
+  }
+
   /// isNotDuplicable - Return true if this instruction cannot be safely
   /// duplicated.  For example, if the instruction has a unique labels attached
   /// to it, duplicating it would cause multiple definition errors.