Teach IVUsers to keep things simpler and track loop-invariant strides only

for uses inside the loop. This works better with LSR. Disabled behind
-simplify-iv-users while benchmarking.

llvm-svn: 89299

llvm/lib/Analysis/IVUsers.cpp

@@ -24,6 +24,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/CommandLine.h"
 #include <algorithm>
 using namespace llvm;
 
@@ -31,6 +32,10 @@ char IVUsers::ID = 0;
 static RegisterPass<IVUsers>
 X("iv-users", "Induction Variable Users", false, true);
 
+static cl::opt<bool>
+SimplifyIVUsers("simplify-iv-users", cl::Hidden, cl::init(false),
+          cl::desc("Restrict IV Users to loop-invariant strides"));
+
 Pass *llvm::createIVUsersPass() {
   return new IVUsers();
 }
@@ -208,6 +213,11 @@ bool IVUsers::AddUsersIfInteresting(Instruction *I) {
   if (!getSCEVStartAndStride(ISE, L, UseLoop, Start, Stride, SE, DT))
     return false;  // Non-reducible symbolic expression, bail out.
 
+  // Keep things simple. Don't touch loop-variant strides.
+  if (SimplifyIVUsers && !Stride->isLoopInvariant(L)
+      && L->contains(I->getParent()))
+    return false;
+
   SmallPtrSet<Instruction *, 4> UniqueUsers;
   for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
        UI != E; ++UI) {