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



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238051 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/CommandFlags.h

@@ -24,6 +24,7 @@
 #include "llvm/Support/Host.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetOptions.h"
+#include "llvm/Target/TargetRecip.h"
 #include <string>
 using namespace llvm;
 
@@ -152,6 +153,12 @@ FuseFPOps("fp-contract",
                          "Only fuse FP ops when the result won't be effected."),
               clEnumValEnd));
 
+cl::list<std::string>
+ReciprocalOps("recip",
+  cl::CommaSeparated,
+  cl::desc("Choose reciprocal operation types and parameters."),
+  cl::value_desc("all,none,default,divf,!vec-sqrtd,vec-divd:0,sqrt:9..."));
+
 cl::opt<bool>
 DontPlaceZerosInBSS("nozero-initialized-in-bss",
               cl::desc("Don't place zero-initialized symbols into bss section"),
@@ -231,6 +238,7 @@ static inline TargetOptions InitTargetOptionsFromCodeGenFlags() {
   Options.LessPreciseFPMADOption = EnableFPMAD;
   Options.NoFramePointerElim = DisableFPElim;
   Options.AllowFPOpFusion = FuseFPOps;
+  Options.Reciprocals = ReciprocalOps;
   Options.UnsafeFPMath = EnableUnsafeFPMath;
   Options.NoInfsFPMath = EnableNoInfsFPMath;
   Options.NoNaNsFPMath = EnableNoNaNsFPMath;