make reciprocal estimate code generation more flexible by adding command-line options (2nd try)

The first try (r238051) to land this was reverted due to bot failures
that were hopefully addressed by r238788.

This patch adds a TargetRecip class for processing many recip codegen possibilities.
The 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 x86 CPUs continue to *not* use reciprocal estimates by default with -ffast-math.

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

llvm-svn: 238842

1 files changed, 0 insertions, 2 deletions

diff --git a/llvm/lib/Target/X86/X86Subtarget.cpp b/llvm/lib/Target/X86/X86Subtarget.cpp
index 1cdab14e034..65e702e7f35 100644
--- a/llvm/lib/Target/X86/X86Subtarget.cpp
+++ b/llvm/lib/Target/X86/X86Subtarget.cpp
@@ -273,8 +273,6 @@ void X86Subtarget::initializeEnvironment() {
   LEAUsesAG = false;
   SlowLEA = false;
   SlowIncDec = false;
-  UseSqrtEst = false;
-  UseReciprocalEst = false;
   stackAlignment = 4;
   // FIXME: this is a known good value for Yonah. How about others?
   MaxInlineSizeThreshold = 128;