[X86] Tune LEA usage for Silvermont

According to Intel Software Optimization Manual on Silvermont in some cases LEA
is better to be replaced with ADD instructions:
"The rule of thumb for ADDs and LEAs is that it is justified to use LEA
with a valid index and/or displacement for non-destructive destination purposes
(especially useful for stack offset cases), or to use a SCALE.
Otherwise, ADD(s) are preferable."

Differential Revision: http://reviews.llvm.org/D3826

llvm-svn: 209198

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/X86TargetMachine.cpp b/llvm/lib/Target/X86/X86TargetMachine.cpp
index cb5ab0d..d0449f4 100644
--- a/llvm/lib/Target/X86/X86TargetMachine.cpp
+++ b/llvm/lib/Target/X86/X86TargetMachine.cpp
@@ -226,7 +226,8 @@ bool X86PassConfig::addPreEmitPass() {
     ShouldPrint = true;
   }
   if (getOptLevel() != CodeGenOpt::None &&
-      getX86Subtarget().LEAusesAG()){
+      (getX86Subtarget().LEAusesAG() ||
+       getX86Subtarget().slowLEA())){
     addPass(createX86FixupLEAs());
     ShouldPrint = true;
   }