Handle cast instructions in complete loop unroll heuristic.

[mzolotukhin]

Summary

Cast instructions are important to handle since induction variables are often extended to 64-bits.
This patch is intended to be applied after D10205 (though it could be applied independently with minor changes).

[mzolotukhin]

• Don't try to const-prop casts if the simplified value is just an offset from a base pointer.

[chandlerc]

No test case here? Is this covered by the tests in D10208?

lib/Transforms/Scalar/LoopUnrollPass.cpp

446–450

I think the need for this will go away when offsets aren't (incorrectly) marked as needed in SimplifiedValues. See my comments is D10205.

452

This doesn't seem to be specific to ptrtoint. =]

[mzolotukhin]

• Fallback to Base visitor if failed to constant fold (and only then call simplifyInstWithSCEV).
• Add TODO to visitCast.

[mzolotukhin]

No test case here? Is this covered by the tests in D10208?

Yes, all tests are in D10208.

[mzolotukhin]

Ping!

[mzolotukhin]

Ping!

[mzolotukhin]

Ping!

[chandlerc]

This patch looks fine, but I'd like to have a test case that specifically exercises it. Is that possible given the current state, or does that come in a subsequent patch?

lib/Transforms/Scalar/LoopUnrollPass.cpp

444

This comment still seems stale (referring to ptrtoint).

[chandlerc]

Just as a note, this LGTM provided a minimal test change is included when it is committed.

[mzolotukhin]

Thanks!

I added a new test here and committed the patch (with comment fixed too) in r242257.

lib/Transforms/Scalar/LoopUnrollPass.cpp

bool visitLoad(LoadInst &I) {
 
     Constant *CV = CDS->getElementAsConstant(Index);
     assert(CV && "Constant expected.");
     SimplifiedValues[&I] = CV;
 
     return true;
   }
 
+  bool visitCastInst(CastInst &I) {
+    // Propagate constants through ptrtoint.
+    Constant *COp = dyn_cast<Constant>(I.getOperand(0));
+    if (!COp)
+      COp = SimplifiedValues.lookup(I.getOperand(0));
+    // TODO: If we do ptrtoint of an expression, which is present in
+    // SimplifiedOffsets, we can propagate this information.
+    if (COp)
+      if (Constant *C =
+              ConstantExpr::getCast(I.getOpcode(), COp, I.getType())) {
+        SimplifiedValues[&I] = C;
+        return true;
+      }
+
+    return Base::visitCastInst(I);
+  }
+
   bool visitCmpInst(CmpInst &I) {
     Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
 
     // First try to handle simplified comparisons.
     if (!isa<Constant>(LHS))
       if (Constant *SimpleLHS = SimplifiedValues.lookup(LHS))
         LHS = SimpleLHS;
     if (!isa<Constant>(RHS))