[llvm] r214957 - [AArch64] Conditional selects are expensive on out-of-order cores.

[James Molloy]

Author: jamesm
Date: Wed Aug  6 05:42:18 2014
New Revision: 214957

URL: http://llvm.org/viewvc/llvm-project?rev=214957&view=rev
Log:
[AArch64] Conditional selects are expensive on out-of-order cores.

Specifically Cortex-A57. This probably applies to Cyclone too but I haven't enabled it for that as I can't test it.

This gives ~4% improvement on SPEC 174.vpr, and ~1% in 471.omnetpp.

Modified:
    llvm/trunk/lib/Target/AArch64/AArch64ISelLowering.cpp

Modified: llvm/trunk/lib/Target/AArch64/AArch64ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AArch64/AArch64ISelLowering.cpp?rev=214957&r1=214956&r2=214957&view=diff
==============================================================================
--- llvm/trunk/lib/Target/AArch64/AArch64ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/AArch64/AArch64ISelLowering.cpp Wed Aug  6 05:42:18 2014
@@ -477,6 +477,10 @@ AArch64TargetLowering::AArch64TargetLowe
       setOperationAction(ISD::FROUND, Ty, Legal);
     }
   }
+
+  // Prefer likely predicted branches to selects on out-of-order cores.
+  if (Subtarget->isCortexA57())
+    PredictableSelectIsExpensive = true;
 }
 
 void AArch64TargetLowering::addTypeForNEON(EVT VT, EVT PromotedBitwiseVT) {