[PATCH] Have HasSideEffects() return false for __attribute__((const)) functions

[Kuperstein, Michael M]

I think PureAttr isn't strong enough.

char foo(char *a)
{
   return *a;
}

is pure, but isn't side-effect free.

-----Original Message-----
From: hfinkel at anl.gov [mailto:hfinkel at anl.gov] 
Sent: Monday, March 23, 2015 18:20
To: Kuperstein, Michael M; richard at metafoo.co.uk; aaron.ballman at gmail.com; hfinkel at anl.gov
Cc: cfe-commits at cs.uiuc.edu
Subject: Re: [PATCH] Have HasSideEffects() return false for __attribute__((const)) functions

================
Comment at: lib/AST/Expr.cpp:2953
@@ +2952,3 @@
+    const Decl *FD = cast<CallExpr>(this)->getCalleeDecl();
+    bool IsConst = FD && FD->hasAttr<ConstAttr>();
+    if (IsConst || !IncludePossibleEffects)
----------------
You're checking for ConstAttr here, which is fine, but I think that we can do more:

This is allowed:
  static int i;
  void foo() {
    __builtin_assume(i > 0);
  }

and so we can also check for PureAttr. And what about constexpr functions?

http://reviews.llvm.org/D8548

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