Reapply r233175 and r233183: float2int.

This re-adds float2int to the tree, after fixing PR23038. It turns
out the argument to APSInt() is true-if-unsigned, rather than
true-if-signed :(. Added testcase and explanatory comment.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233370 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/InitializePasses.h

@@ -294,6 +294,7 @@ void initializeWinEHPreparePass(PassRegistry&);
 void initializePlaceBackedgeSafepointsImplPass(PassRegistry&);
 void initializePlaceSafepointsPass(PassRegistry&);
 void initializeDwarfEHPreparePass(PassRegistry&);
+void initializeFloat2IntPass(PassRegistry&);
 }
 
 #endif

include/llvm/LinkAllPasses.h

@@ -169,6 +169,7 @@ namespace {
       (void) llvm::createRewriteSymbolsPass();
       (void) llvm::createStraightLineStrengthReducePass();
       (void) llvm::createMemDerefPrinter();
+      (void) llvm::createFloat2IntPass();
 
       (void)new llvm::IntervalPartition();
       (void)new llvm::ScalarEvolution();

include/llvm/Transforms/Scalar.h

@@ -446,6 +446,12 @@ ModulePass *createPlaceSafepointsPass();
 //
 FunctionPass *createRewriteStatepointsForGCPass();
 
+//===----------------------------------------------------------------------===//
+//
+// Float2Int - Demote floats to ints where possible.
+//
+FunctionPass *createFloat2IntPass();
+
 } // End llvm namespace
 
 #endif

lib/Transforms/IPO/PassManagerBuilder.cpp

@@ -59,6 +59,10 @@ static cl::opt<bool>
 RunLoopRerolling("reroll-loops", cl::Hidden,
                  cl::desc("Run the loop rerolling pass"));
 
+static cl::opt<bool>
+RunFloat2Int("float-to-int", cl::Hidden, cl::init(true),
+             cl::desc("Run the float2int (float demotion) pass"));
+
 static cl::opt<bool> RunLoadCombine("combine-loads", cl::init(false),
                                     cl::Hidden,
                                     cl::desc("Run the load combining pass"));
@@ -307,6 +311,9 @@ void PassManagerBuilder::populateModulePassManager(
   // we must insert a no-op module pass to reset the pass manager.
   MPM.add(createBarrierNoopPass());
 
+  if (RunFloat2Int)
+    MPM.add(createFloat2IntPass());
+
   // Re-rotate loops in all our loop nests. These may have fallout out of
   // rotated form due to GVN or other transformations, and the vectorizer relies
   // on the rotated form.

lib/Transforms/Scalar/CMakeLists.txt

@@ -9,6 +9,7 @@ add_llvm_library(LLVMScalarOpts
   DeadStoreElimination.cpp
   EarlyCSE.cpp
   FlattenCFGPass.cpp
+  Float2Int.cpp
   GVN.cpp
   InductiveRangeCheckElimination.cpp
   IndVarSimplify.cpp