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

[Richard Smith]

================
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)
----------------
hfinkel wrote:
> 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?
> 
I don't think we can do anything interesting for `constexpr` functions, because they're not pure in general. One thing you could do is to try to evaluate the expression; if it's a constant expression, then it has no side-effects.

http://reviews.llvm.org/D8548

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