[LowerConstantIntrinsics] reuse isManifestLogic from ConstantFolding

GlobalVariables are Constants, yet should not unconditionally be
considered true for __builtin_constant_p.

Via the LangRef
https://llvm.org/docs/LangRef.html#llvm-is-constant-intrinsic:

    This intrinsic generates no code. If its argument is known to be a
    manifest compile-time constant value, then the intrinsic will be
    converted to a constant true value. Otherwise, it will be converted
    to a constant false value.

    In particular, note that if the argument is a constant expression
    which refers to a global (the address of which _is_ a constant, but
    not manifest during the compile), then the intrinsic evaluates to
    false.

Move isManifestConstant from ConstantFolding to be a method of
Constant so that we can reuse the same logic in
LowerConstantIntrinsics.

pr/41459

Reviewed By: rsmith, george.burgess.iv

Differential Revision: https://reviews.llvm.org/D102367

Author: nickdesaulniers

llvm/include/llvm/IR/Constant.h

@@ -217,6 +217,10 @@ class Constant : public User {
   /// changes are made, the constant C is returned.
   static Constant *mergeUndefsWith(Constant *C, Constant *Other);
 
+  /// Return true if a constant is ConstantData or a ConstantAggregate or
+  /// ConstantExpr that contain only ConstantData.
+  bool isManifestConstant() const;
+
 private:
   enum PossibleRelocationsTy {
     /// This constant requires no relocations. That is, it holds simple

llvm/lib/Analysis/ConstantFolding.cpp

@@ -1806,19 +1806,6 @@ double getValueAsDouble(ConstantFP *Op) {
   return APF.convertToDouble();
 }
 
-static bool isManifestConstant(const Constant *c) {
-  if (isa<ConstantData>(c)) {
-    return true;
-  } else if (isa<ConstantAggregate>(c) || isa<ConstantExpr>(c)) {
-    for (const Value *subc : c->operand_values()) {
-      if (!isManifestConstant(cast<Constant>(subc)))
-        return false;
-    }
-    return true;
-  }
-  return false;
-}
-
 static bool getConstIntOrUndef(Value *Op, const APInt *&C) {
   if (auto *CI = dyn_cast<ConstantInt>(Op)) {
     C = &CI->getValue();
@@ -1843,7 +1830,7 @@ static Constant *ConstantFoldScalarCall1(StringRef Name,
     // We know we have a "Constant" argument. But we want to only
     // return true for manifest constants, not those that depend on
     // constants with unknowable values, e.g. GlobalValue or BlockAddress.
-    if (isManifestConstant(Operands[0]))
+    if (Operands[0]->isManifestConstant())
       return ConstantInt::getTrue(Ty->getContext());
     return nullptr;
   }

llvm/lib/IR/Constants.cpp

@@ -823,6 +823,18 @@ Constant *Constant::mergeUndefsWith(Constant *C, Constant *Other) {
   return C;
 }
 
+bool Constant::isManifestConstant() const {
+  if (isa<ConstantData>(this))
+    return true;
+  if (isa<ConstantAggregate>(this) || isa<ConstantExpr>(this)) {
+    for (const Value *Op : operand_values())
+      if (!cast<Constant>(Op)->isManifestConstant())
+        return false;
+    return true;
+  }
+  return false;
+}
+
 //===----------------------------------------------------------------------===//
 //                                ConstantInt
 //===----------------------------------------------------------------------===//

llvm/lib/Transforms/Scalar/LowerConstantIntrinsics.cpp

@@ -45,10 +45,10 @@ STATISTIC(ObjectSizeIntrinsicsHandled,
           "Number of 'objectsize' intrinsic calls handled");
 
 static Value *lowerIsConstantIntrinsic(IntrinsicInst *II) {
-  Value *Op = II->getOperand(0);
-
-  return isa<Constant>(Op) ? ConstantInt::getTrue(II->getType())
-                           : ConstantInt::getFalse(II->getType());
+  if (auto *C = dyn_cast<Constant>(II->getOperand(0)))
+    if (C->isManifestConstant())
+      return ConstantInt::getTrue(II->getType());
+  return ConstantInt::getFalse(II->getType());
 }
 
 static bool replaceConditionalBranchesOnConstant(Instruction *II,

llvm/test/Transforms/LowerConstantIntrinsics/constant-intrinsics.ll

@@ -112,3 +112,11 @@ define i1 @test_various_types(i256 %int, float %float, <2 x i64> %vec, {i32, i32
 
   ret i1 %res6
 }
+
+@real_mode_blob_end = external dso_local global [0 x i8], align 1
+define i1 @global_array() {
+; CHECK-LABEL: @global_array(
+; CHECK-NEXT: ret i1 false
+  %1 = call i1 @llvm.is.constant.i64(i64 ptrtoint ([0 x i8]* @real_mode_blob_end to i64))
+  ret i1 %1
+}