[Float2Int] Make iteration over Roots deterministic

[bjope]

Summary

Use a SmallSetVector instead of a SmallPtrSet when collecting
and storing Roots.

The iteration order for a SmallPtrSet is not deterministic,
so in the past the order of items inserted in the WorkList
inside walkBackwards has been non-deterministic. This patch
intends to make the order of rewrites done in Float2Int
deterministic by changing the container for the Roots set.

The semantics result of the transformation should not be
any different afaict. But at least naming of IR variables
(when outputting the result as an ll file) should be more
stable now.

[bjope]

(not sure whom to add as reviewer to patches like this, added some random people who has contributed to this pass earlier)

Also see https://reviews.llvm.org/D74533 for a preparatory cleanup patch.

[bjope]

Removed the need for D74533 as pre-commit, by removing the passing of
the Roots member variable as argument to member functions.

[spatel]

llvm/lib/Transforms/Scalar/Float2Int.cpp

527–529 ↗

(On Diff #256725)

Isn't the change use the member variable directly (rather than passing a param to it) truly NFC?
IIUC, we should make that change first (no need for pre-commit review).

[bjope]

Rebased after pre-commit of the cleanup (we no longer pass around references to Roots).

[spatel]

I'd say we reduced this as much as possible. :)
LGTM

llvm/include/llvm/Transforms/Scalar/Float2Int.h

 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_TRANSFORMS_SCALAR_FLOAT2INT_H
 #define LLVM_TRANSFORMS_SCALAR_FLOAT2INT_H
 
 #include "llvm/ADT/EquivalenceClasses.h"
 #include "llvm/ADT/MapVector.h"
+#include "llvm/ADT/SetVector.h"
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/PassManager.h"
 
 namespace llvm {
 class Float2IntPass : public PassInfoMixin<Float2IntPass> {
 public:
private:
   ConstantRange validateRange(ConstantRange R);
   void walkBackwards();
   void walkForwards();
   bool validateAndTransform();
   Value *convert(Instruction *I, Type *ToTy);
   void cleanup();
 
   MapVector<Instruction *, ConstantRange> SeenInsts;
-  SmallPtrSet<Instruction *, 8> Roots;
+  SmallSetVector<Instruction *, 8> Roots;
   EquivalenceClasses<Instruction *> ECs;
   MapVector<Instruction *, Value *> ConvertedInsts;
   LLVMContext *Ctx;
 };
 }
 #endif // LLVM_TRANSFORMS_SCALAR_FLOAT2INT_H