make reciprocal estimate code generation more flexible by adding command-line options

This patch adds a class for processing many recip codegen possibilities.
The TargetRecip class is intended to handle both command-line options to llc as well
as options passed in from a front-end such as clang with the -mrecip option.

The x86 backend is updated to use the new functionality.
Only -mcpu=btver2 with -ffast-math should see a functional change from this patch.
All other CPUs continue to *not* use reciprocal estimates by default with -ffast-math.

Differential Revision: http://reviews.llvm.org/D8982

llvm-svn: 238051

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86TargetMachine.cpp b/llvm/lib/Target/X86/X86TargetMachine.cpp
index 3e5f1d82202..33576f1771f 100644
--- a/llvm/lib/Target/X86/X86TargetMachine.cpp
+++ b/llvm/lib/Target/X86/X86TargetMachine.cpp
@@ -105,6 +105,13 @@ X86TargetMachine::X86TargetMachine(const Target &T, StringRef TT, StringRef CPU,
   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);
+
   initAsmInfo();
 }