[MemoryBuiltin] Add an API for checking if an unused allocation can be removed [NFC]

Not all allocation functions are removable if unused.  An example of a non-removable allocation would be a direct call to the replaceable global allocation function in C++.  An example of a removable one - at least according to historical practice - would be malloc.

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/MemoryBuiltins.cpp b/llvm/lib/Analysis/MemoryBuiltins.cpp
index 213fdc5a..48c01fb 100644
--- a/llvm/lib/Analysis/MemoryBuiltins.cpp
+++ b/llvm/lib/Analysis/MemoryBuiltins.cpp
@@ -298,6 +298,17 @@ bool llvm::isStrdupLikeFn(const Value *V, const TargetLibraryInfo *TLI) {
   return getAllocationData(V, StrDupLike, TLI).hasValue();
 }
 
+bool llvm::isAllocRemovable(const CallBase *CB, const TargetLibraryInfo *TLI) {
+  assert(isAllocationFn(CB, TLI));
+
+  // Note: Removability is highly dependent on the source language.  For
+  // example, recent C++ requires direct calls to the global allocation
+  // [basic.stc.dynamic.allocation] to be observable unless part of a new
+  // expression [expr.new paragraph 13].
+
+  // Historically we've treated the C family allocation routines as removable
+  return isAllocLikeFn(CB, TLI);
+}
 
 Value *llvm::getAllocAlignment(const CallBase *V,
                                const TargetLibraryInfo *TLI) {