indvars: Added DisableIVRewrite and WidenIVs.

This adds functionality to remove size/zero extension during indvars
without generating a canonical IV and rewriting all IV users. It's
disabled by default so should have no effect on codegen. Work in progress.

llvm-svn: 130829

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/IVUsers.cpp b/llvm/lib/Analysis/IVUsers.cpp
index 2cda7913f02..a8fe5458263 100644
--- a/llvm/lib/Analysis/IVUsers.cpp
+++ b/llvm/lib/Analysis/IVUsers.cpp
@@ -21,6 +21,7 @@
 #include "llvm/Analysis/Dominators.h"
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Assembly/Writer.h"
 #include "llvm/ADT/STLExtras.h"
@@ -38,6 +39,15 @@ INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
 INITIALIZE_PASS_END(IVUsers, "iv-users",
                       "Induction Variable Users", false, true)
 
+// IVUsers behavior currently depends on this temporary indvars mode. The
+// option must be defined upstream from its uses.
+namespace llvm {
+  bool DisableIVRewrite = false;
+}
+cl::opt<bool, true> DisableIVRewriteOpt(
+  "disable-iv-rewrite", cl::Hidden, cl::location(llvm::DisableIVRewrite),
+  cl::desc("Disable canonical induction variable rewriting"));
+
 Pass *llvm::createIVUsersPass() {
   return new IVUsers();
 }
@@ -90,6 +100,11 @@ bool IVUsers::AddUsersIfInteresting(Instruction *I) {
   if (Width > 64 || (TD && !TD->isLegalInteger(Width)))
     return false;
 
+  // We expect Sign/Zero extension to be eliminated from the IR before analyzing
+  // any downstream uses.
+  if (DisableIVRewrite && (isa<SExtInst>(I) || isa<ZExtInst>(I)))
+    return false;
+
   if (!Processed.insert(I))
     return true;    // Instruction already handled.