[x86] set default reciprocal (division and square root) codegen to match GCC

D8982 ( checked in at http://reviews.llvm.org/rL239001 ) added command-line 
options to allow reciprocal estimate instructions to be used in place of
divisions and square roots.

This patch changes the default settings for x86 targets to allow that recip
codegen (except for scalar division because that breaks too much code) when
using -ffast-math or its equivalent. 

This matches GCC behavior for this kind of codegen.

Differential Revision: http://reviews.llvm.org/D10396

llvm-svn: 240310

1 files changed, 9 insertions, 6 deletions

diff --git a/llvm/lib/Target/X86/X86TargetMachine.cpp b/llvm/lib/Target/X86/X86TargetMachine.cpp
index 3d6eb4f7ce0..fb9cb4ba4c8 100644
--- a/llvm/lib/Target/X86/X86TargetMachine.cpp
+++ b/llvm/lib/Target/X86/X86TargetMachine.cpp
@@ -110,12 +110,15 @@ X86TargetMachine::X86TargetMachine(const Target &T, const Triple &TT,
   if (Subtarget.isTargetWin64())
     this->Options.TrapUnreachable = true;
 
-  // TODO: By default, all reciprocal estimate operations are off because
-  // that matches the behavior before TargetRecip was added (except for btver2
-  // which used subtarget features to enable this type of codegen).
-  // We should change this to match GCC behavior where everything but
-  // scalar division estimates are turned on by default with -ffast-math.
-  this->Options.Reciprocals.setDefaults("all", false, 1);
+  // By default (and when -ffast-math is on), enable estimate codegen for
+  // everything except scalar division. By default, use 1 refinement step for
+  // all operations. Defaults may be overridden by using command-line options.
+  // Scalar division estimates are disabled because they break too much
+  // real-world code. These defaults match GCC behavior.
+  this->Options.Reciprocals.setDefaults("sqrtf", true, 1);
+  this->Options.Reciprocals.setDefaults("divf", false, 1);
+  this->Options.Reciprocals.setDefaults("vec-sqrtf", true, 1);
+  this->Options.Reciprocals.setDefaults("vec-divf", true, 1);
 
   initAsmInfo();
 }