[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

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index 7d93d41..54b0a7d 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/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
 //===----------------------------------------------------------------------===//