[PATCH] D78148: [CodeGen] make isTriviallyRecursive handle more trivial recursion

[George Burgess IV via Phabricator via cfe-commits]

george.burgess.iv created this revision.
george.burgess.iv added reviewers: efriedma, serge-sans-paille.
george.burgess.iv added a project: clang.
Herald added a subscriber: cfe-commits.

This function was not catching all forms of trivial recursion, meaning:

  void *memcpy(void *a, const void *b, size_t n) {
    return __builtin_memcpy(a, b, n);
  }

would be considered trivially recursive, whereas

  void *memcpy(void *a, const void *b, size_t n) {
    return memcpy(a, b, n);
  }

would not.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D78148

Files:
  clang/lib/CodeGen/CodeGenModule.cpp
  clang/test/CodeGen/memcpy-no-emission-trivial-recursion.c


Index: clang/test/CodeGen/memcpy-no-emission-trivial-recursion.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/memcpy-no-emission-trivial-recursion.c
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -S -emit-llvm -o - %s | FileCheck %s
+//
+// Verifies that clang doesn't emit trivially-recursive extern inline functions.
+
+typedef unsigned long size_t;
+
+// always_inline is used so clang will emit any available_externally function in
+// -O0.
+#define AVAILABLE_EXTERNALLY extern inline __attribute__((always_inline)) \
+    __attribute__((gnu_inline))
+
+void some_other_fn(void);
+
+AVAILABLE_EXTERNALLY void *some_fn() {
+  some_other_fn();
+  return some_fn();
+}
+
+// CHECK-LABEL: define void @foo
+void foo() {
+  // CHECK-NOT: call void @some_other_fn
+  some_fn();
+}
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -2651,15 +2651,19 @@
 namespace {
   struct FunctionIsDirectlyRecursive
       : public ConstStmtVisitor<FunctionIsDirectlyRecursive, bool> {
+    const FunctionDecl *OriginalFD;
     const StringRef Name;
     const Builtin::Context &BI;
-    FunctionIsDirectlyRecursive(StringRef N, const Builtin::Context &C)
-        : Name(N), BI(C) {}
+    FunctionIsDirectlyRecursive(const FunctionDecl *OriginalFD, StringRef N,
+                                const Builtin::Context &C)
+        : OriginalFD(OriginalFD), Name(N), BI(C) {}
 
     bool VisitCallExpr(const CallExpr *E) {
       const FunctionDecl *FD = E->getDirectCallee();
       if (!FD)
         return false;
+      if (FD == OriginalFD)
+        return true;
       AsmLabelAttr *Attr = FD->getAttr<AsmLabelAttr>();
       if (Attr && Name == Attr->getLabel())
         return true;
@@ -2762,7 +2766,7 @@
     Name = FD->getName();
   }
 
-  FunctionIsDirectlyRecursive Walker(Name, Context.BuiltinInfo);
+  FunctionIsDirectlyRecursive Walker(FD, Name, Context.BuiltinInfo);
   const Stmt *Body = FD->getBody();
   return Body ? Walker.Visit(Body) : false;
 }


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