[Bug c++/17972] [3.4 Regression] const/pure functions result in bad asm

["ebotcazou at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From ebotcazou at gcc dot gnu dot org  2005-03-03 19:25 -------
> It really seems like the C++ front end is doing the right thing, 
> abstractly -- these functions don't have side-effects!  So, either the 
> inliner or stabilize reference seems like it needs fixing.  Maybe the 
> latter should recognize CALL_EPRs?

I agree that the C++ FE is theoritically right, but other FEs appear to already
have realized that the implementation constraints trumpet the theory here: on
mainline, the C, Java and Fortran 95 FEs set TREE_SIDE_EFFECTS on CALL_EXPRs.

I think it is too late to fix the problem in the tree inliner because it would
be tricky to detect there whether a CALL_EXPR is mentioned more than once.

Special-casing CALL_EXPRs in stabilize_reference could indeed be the solution. 
We could even be clever and check whether tree inlining is enabled and, if so,
whether it has already occurred.  Does that sound plausible?

> If it's not possible to fix this, then what we should do is modify 
> build3 to mark CALL_EXPRs as having side-effects.  Right now, it makrs 
> them based on the flags for the function, so this problem isn't really 
> C++-specific; it probably effects all languages except those whose front 
> ends set TREE_SIDE_EFFECTS additionally themselves.  (Unless C++ is 
> changing out the operands to the CALL_EXPR after its created.)

Right.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17972