[IR] Redefine Freeze instruction

Summary:
This patch redefines freeze instruction from being UnaryOperator to a subclass of UnaryInstruction.

ConstantExpr freeze is removed, as discussed in the previous review.
FreezeOperator is not added because there's no ConstantExpr freeze.
`freeze i8* null` test is added to `test/Bindings/llvm-c/freeze.ll` as well, because the null pointer-related bug in `tools/llvm-c/echo.cpp` is now fixed.
InstVisitor has visitFreeze now because freeze is not unaryop anymore.

Reviewers: whitequark, deadalnix, craig.topper, jdoerfert, lebedev.ri

Reviewed By: craig.topper, lebedev.ri

Subscribers: regehr, nlopes, mehdi_amini, hiraditya, steven_wu, dexonsmith, jfb, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69932

2 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 914edad0b8b..18fef7db9c7 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -10593,7 +10593,7 @@ void SelectionDAGBuilder::visitSwitch(const SwitchInst &SI) {
   }
 }
 
-void SelectionDAGBuilder::visitFreeze(const User &I) {
+void SelectionDAGBuilder::visitFreeze(const FreezeInst &I) {
   SDValue N = getValue(I.getOperand(0));
   setValue(&I, N);
 }
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
index c288a4f6908..1579ef3ad75 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
@@ -668,7 +668,6 @@ private:
 
   void visitUnary(const User &I, unsigned Opcode);
   void visitFNeg(const User &I) { visitUnary(I, ISD::FNEG); }
-  void visitFreeze(const User &I);
 
   void visitBinary(const User &I, unsigned Opcode);
   void visitShift(const User &I, unsigned Opcode);
@@ -743,6 +742,7 @@ private:
   void visitAtomicStore(const StoreInst &I);
   void visitLoadFromSwiftError(const LoadInst &I);
   void visitStoreToSwiftError(const StoreInst &I);
+  void visitFreeze(const FreezeInst &I);
 
   void visitInlineAsm(ImmutableCallSite CS);
   void visitIntrinsicCall(const CallInst &I, unsigned Intrinsic);