instcombine: Migrate math library call simplifications

This patch migrates the math library call simplifications from the
simplify-libcalls pass into the instcombine library call simplifier.

I have typically migrated just one simplifier at a time, but the math
simplifiers are interdependent because:

   1. CosOpt, PowOpt, and Exp2Opt all depend on UnaryDoubleFPOpt.
   2. CosOpt, PowOpt, Exp2Opt, and UnaryDoubleFPOpt all depend on
      the option -enable-double-float-shrink.

These two factors made migrating each of these simplifiers individually
more of a pain than it would be worth.  So, I migrated them all together.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167815 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -44,6 +44,7 @@
 #include "llvm/Target/TargetLibraryInfo.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Support/CFG.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/GetElementPtrTypeIterator.h"
 #include "llvm/Support/PatternMatch.h"
@@ -65,6 +66,11 @@ STATISTIC(NumExpand,    "Number of expansions");
 STATISTIC(NumFactor   , "Number of factorizations");
 STATISTIC(NumReassoc  , "Number of reassociations");
 
+static cl::opt<bool> UnsafeFPShrink("enable-double-float-shrink", cl::Hidden,
+                                   cl::init(false),
+                                   cl::desc("Enable unsafe double to float "
+                                            "shrinking for math lib calls"));
+
 // Initialization Routines
 void llvm::initializeInstCombine(PassRegistry &Registry) {
   initializeInstCombinerPass(Registry);
@@ -2374,7 +2380,7 @@ public:
   InstCombinerLibCallSimplifier(const DataLayout *TD,
                                 const TargetLibraryInfo *TLI,
                                 InstCombiner *IC)
-    : LibCallSimplifier(TD, TLI) {
+    : LibCallSimplifier(TD, TLI, UnsafeFPShrink) {
     this->IC = IC;
   }