[Polly] [ManagedMemoryRewrite] Iterate over operands of the expanded instruction, not the constantexpr itself.

[bollu]

Summary

• We should iterate over I, which is Cur expanded out to an

instruction, and not Cur itself.

[bollu]

• Invalidate Cur by deleting it and setting it to nullptr

lib/CodeGen/ManagedMemoryRewrite.cpp

139

Not sure if this is sane. Thoughts?

[grosser]

LGTM, only some minor comments.

lib/CodeGen/ManagedMemoryRewrite.cpp

125

Deleting does not seem to be save.

149

Empty line.

[bollu]

• Don't call DeleteValue on the ConstantExpr because there can be multiple use sites

[bollu]

• [NFC] remove empty line

[bollu]

• [NFC] reorder statements

[grosser]

LGTM

lib/CodeGen/ManagedMemoryRewrite.cpp

 // D  D
 // TODO: We don't _have_to do this, but this is the simplest solution.
 // We can write a solution that keeps track of which constants have been
 // already expanded.
 static void expandConstantExpr(ConstantExpr *Cur, PollyIRBuilder &Builder,
                                Instruction *Parent, int index,
                                SmallPtrSet<Instruction *, 4> &Expands) {
   assert(Cur && "invalid constant expression passed");
-
   Instruction *I = Cur->getAsInstruction();
+  assert(I && "unable to convert ConstantExpr to Instruction");
+
+  DEBUG(dbgs() << "Expanding ConstantExpression: " << *Cur
+               << " | in Instruction: " << *I << "\n";);
+
+  // Invalidate `Cur` so that no one after this point uses `Cur`. Rather,
+  // they should mutate `I`.
+  Cur = nullptr;
+
   Expands.insert(I);
   Parent->setOperand(index, I);
 
-  assert(I && "unable to convert ConstantExpr to Instruction");
   // The things that `Parent` uses (its operands) should be created
   // before `Parent`.
   Builder.SetInsertPoint(Parent);
   Builder.Insert(I);
 
-  DEBUG(dbgs() << "Expanding ConstantExpression: " << *Cur
-               << " | in Instruction: " << *I << "\n";);
-  for (unsigned i = 0; i < Cur->getNumOperands(); i++) {
-    Value *Op = Cur->getOperand(i);
+  for (unsigned i = 0; i < I->getNumOperands(); i++) {
+    Value *Op = I->getOperand(i);
     assert(isa<Constant>(Op) && "constant must have a constant operand");
 
     if (ConstantExpr *CExprOp = dyn_cast<ConstantExpr>(Op))
       expandConstantExpr(CExprOp, Builder, I, i, Expands);
   }
 }
 
 // Edit all uses of `OldVal` to NewVal` in `Inst`. This will rewrite
 // `ConstantExpr`s that are used in the `Inst`.
 // Note that `replaceAllUsesWith` is insufficient for this purpose because it
 // does not rewrite values in `ConstantExpr`s.
 static void rewriteOldValToNew(Instruction *Inst, Value *OldVal, Value *NewVal,
                                PollyIRBuilder &Builder) {