[CodeGen] Add a pass to fold null checks into nearby memory operations.

Summary:
This change adds an "ImplicitNullChecks" target dependent pass.  This
pass folds null checks into memory operation using the FAULTING_LOAD
pseudo-op introduced in previous patches.

Depends on D10197
Depends on D10199
Depends on D10200

Reviewers: reames, rnk, pgavlin, JosephTremoulet, atrick

Reviewed By: atrick

Subscribers: ab, JosephTremoulet, llvm-commits

Differential Revision: http://reviews.llvm.org/D10201

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239743 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/Passes.cpp

@@ -72,6 +72,10 @@ static cl::opt<bool> DisableCopyProp("disable-copyprop", cl::Hidden,
     cl::desc("Disable Copy Propagation pass"));
 static cl::opt<bool> DisablePartialLibcallInlining("disable-partial-libcall-inlining",
     cl::Hidden, cl::desc("Disable Partial Libcall Inlining"));
+static cl::opt<bool> EnableImplicitNullChecks(
+    "enable-implicit-null-checks",
+    cl::desc("Fold null checks into faulting memory operations"),
+    cl::init(false));
 static cl::opt<bool> PrintLSR("print-lsr-output", cl::Hidden,
     cl::desc("Print LLVM IR produced by the loop-reduce pass"));
 static cl::opt<bool> PrintISelInput("print-isel-input", cl::Hidden,
@@ -543,6 +547,9 @@ void TargetPassConfig::addMachinePasses() {
   // Run pre-sched2 passes.
   addPreSched2();
 
+  if (EnableImplicitNullChecks)
+    addPass(&ImplicitNullChecksID);
+
   // Second pass scheduler.
   if (getOptLevel() != CodeGenOpt::None) {
     if (MISchedPostRA)