[PowerPC] Add Branch Hints for Highly-Biased Branches

This branch adds hints for highly biased branches on the PPC architecture. Even
in absence of profiling information, LLVM will mark code reaching unreachable
terminators and other exceptional control flow constructs as highly unlikely to
be reached.

Patch by Tom Jablin!

llvm-svn: 255398

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCPredicates.h b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCPredicates.h
index 6075631a541..acea600fbb0 100644
--- a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCPredicates.h
+++ b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCPredicates.h
@@ -56,6 +56,14 @@ namespace PPC {
     PRED_BIT_UNSET = 1025
   };
   
+  // Bit for branch taken (plus) or not-taken (minus) hint
+  enum BranchHintBit {
+    BR_NO_HINT       = 0x0,
+    BR_NONTAKEN_HINT = 0x2,
+    BR_TAKEN_HINT    = 0x3,
+    BR_HINT_MASK     = 0X3
+  };
+
   /// Invert the specified predicate.  != -> ==, < -> >=.
   Predicate InvertPredicate(Predicate Opcode);