Re: [PATCH] [RFC] RAII auto_mpfr and autp_mpz

[Richard Biener <rguenther@suse.de>]

On Mon, 6 Mar 2023, Jonathan Wakely wrote:

> On Mon, 6 Mar 2023 at 10:11, Richard Biener <rguenther@suse.de> wrote:
> >
> > The following adds two RAII classes, one for mpz_t and one for mpfr_t
> > making object lifetime management easier.  Both formerly require
> > explicit initialization with {mpz,mpfr}_init and release with
> > {mpz,mpfr}_clear.
> >
> > I've converted two example places (where lifetime is trivial).
> >
> > I've sofar only build cc1 with the change.  Any comments?
> >
> > Thanks,
> > Richard.
> >
> >         * system.h (class auto_mpz): New,
> >         * realmpfr.h (class auto_mpfr): Likewise.
> >         * fold-const-call.cc (do_mpfr_arg1): Use auto_mpfr.
> >         (do_mpfr_arg2): Likewise.
> >         * tree-ssa-loop-niter.cc (bound_difference): Use auto_mpz;
> > ---
> >  gcc/fold-const-call.cc     |  8 ++------
> >  gcc/realmpfr.h             | 15 +++++++++++++++
> >  gcc/system.h               | 14 ++++++++++++++
> >  gcc/tree-ssa-loop-niter.cc | 10 +---------
> >  4 files changed, 32 insertions(+), 15 deletions(-)
> >
> > diff --git a/gcc/fold-const-call.cc b/gcc/fold-const-call.cc
> > index 43819c1f984..fa0b287cc8a 100644
> > --- a/gcc/fold-const-call.cc
> > +++ b/gcc/fold-const-call.cc
> > @@ -130,14 +130,12 @@ do_mpfr_arg1 (real_value *result,
> >
> >    int prec = format->p;
> >    mpfr_rnd_t rnd = format->round_towards_zero ? MPFR_RNDZ : MPFR_RNDN;
> > -  mpfr_t m;
> >
> > -  mpfr_init2 (m, prec);
> > +  auto_mpfr m (prec);
> >    mpfr_from_real (m, arg, MPFR_RNDN);
> >    mpfr_clear_flags ();
> >    bool inexact = func (m, m, rnd);
> >    bool ok = do_mpfr_ckconv (result, m, inexact, format);
> > -  mpfr_clear (m);
> >
> >    return ok;
> >  }
> > @@ -224,14 +222,12 @@ do_mpfr_arg2 (real_value *result,
> >
> >    int prec = format->p;
> >    mpfr_rnd_t rnd = format->round_towards_zero ? MPFR_RNDZ : MPFR_RNDN;
> > -  mpfr_t m;
> >
> > -  mpfr_init2 (m, prec);
> > +  auto_mpfr m (prec);
> >    mpfr_from_real (m, arg1, MPFR_RNDN);
> >    mpfr_clear_flags ();
> >    bool inexact = func (m, arg0.to_shwi (), m, rnd);
> >    bool ok = do_mpfr_ckconv (result, m, inexact, format);
> > -  mpfr_clear (m);
> >
> >    return ok;
> >  }
> > diff --git a/gcc/realmpfr.h b/gcc/realmpfr.h
> > index 5e032c05f25..2db2ecc94d4 100644
> > --- a/gcc/realmpfr.h
> > +++ b/gcc/realmpfr.h
> > @@ -24,6 +24,21 @@
> >  #include <mpfr.h>
> >  #include <mpc.h>
> >
> > +class auto_mpfr
> > +{
> > +public:
> > +  auto_mpfr () { mpfr_init (m_mpfr); }
> > +  explicit auto_mpfr (mpfr_prec_t prec) { mpfr_init2 (m_mpfr, prec); }
> > +  ~auto_mpfr () { mpfr_clear (m_mpfr); }
> > +
> > +  operator mpfr_t& () { return m_mpfr; }
> 
> 
> This implicit conversion makes the following mistake possible, if code
> is incorrectly converted to use it:
> 
> auto_mpfr m (prec);
> // ...
> mpfr_clear (m);  // oops!
> 
> You could prevent that by adding this to the class body:
> 
> friend void mpfr_clear (auto_mpfr&) = delete;
> 
> This will be a better match for calls to mpfr_clear(m) than using the
> implicit conversion then calling the real function, and will give an
> error if used:
> auto.cc:20:13: error: use of deleted function 'void mpfr_clear(auto_mpfr&)'
>
> This deleted friend will not be a candidate for calls to mpfr_clear
> with an argument of any other type, only for calls with an argument of
> type auto_mpfr.

OK, it might be OK to mpfr_clear() twice and/or mpfr_clear/mpfr_init
again.  Quite possibly mpfr_init should get the same treatmen, mixing
auto_* with explicit lifetime management is bad.

> > +
> > +  auto_mpfr (const auto_mpfr &) = delete;
> 
> This class has an implicit-defined assignment operator, which would
> result in a leaks and double-frees.
> You should add:
>    auto_mpfr &operator=(const auto_mpfr &) = delete;
> This ensures it can't becopied by construction or assignment.
> 
> The same two comments apply to auto_mpz.

Thanks a lot, I've adjusted the patch to the one below.

Richard.

From c2736b929a3d0440432f31e65f5c89f4ec9dc21d Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Mon, 6 Mar 2023 11:06:38 +0100
Subject: [PATCH] [RFC] RAII auto_mpfr and autp_mpz
To: gcc-patches@gcc.gnu.org

The following adds two RAII classes, one for mpz_t and one for mpfr_t
making object lifetime management easier.  Both formerly require
explicit initialization with {mpz,mpfr}_init and release with
{mpz,mpfr}_clear.

I've converted two example places (where lifetime is trivial).

	* system.h (class auto_mpz): New,
	* realmpfr.h (class auto_mpfr): Likewise.
	* fold-const-call.cc (do_mpfr_arg1): Use auto_mpfr.
	(do_mpfr_arg2): Likewise.
	* tree-ssa-loop-niter.cc (bound_difference): Use auto_mpz;
---
 gcc/fold-const-call.cc     |  8 ++------
 gcc/realmpfr.h             | 20 ++++++++++++++++++++
 gcc/system.h               | 18 ++++++++++++++++++
 gcc/tree-ssa-loop-niter.cc | 10 +---------
 4 files changed, 41 insertions(+), 15 deletions(-)

diff --git a/gcc/fold-const-call.cc b/gcc/fold-const-call.cc
index 43819c1f984..fa0b287cc8a 100644
--- a/gcc/fold-const-call.cc
+++ b/gcc/fold-const-call.cc
@@ -130,14 +130,12 @@ do_mpfr_arg1 (real_value *result,
 
   int prec = format->p;
   mpfr_rnd_t rnd = format->round_towards_zero ? MPFR_RNDZ : MPFR_RNDN;
-  mpfr_t m;
 
-  mpfr_init2 (m, prec);
+  auto_mpfr m (prec);
   mpfr_from_real (m, arg, MPFR_RNDN);
   mpfr_clear_flags ();
   bool inexact = func (m, m, rnd);
   bool ok = do_mpfr_ckconv (result, m, inexact, format);
-  mpfr_clear (m);
 
   return ok;
 }
@@ -224,14 +222,12 @@ do_mpfr_arg2 (real_value *result,
 
   int prec = format->p;
   mpfr_rnd_t rnd = format->round_towards_zero ? MPFR_RNDZ : MPFR_RNDN;
-  mpfr_t m;
 
-  mpfr_init2 (m, prec);
+  auto_mpfr m (prec);
   mpfr_from_real (m, arg1, MPFR_RNDN);
   mpfr_clear_flags ();
   bool inexact = func (m, arg0.to_shwi (), m, rnd);
   bool ok = do_mpfr_ckconv (result, m, inexact, format);
-  mpfr_clear (m);
 
   return ok;
 }
diff --git a/gcc/realmpfr.h b/gcc/realmpfr.h
index 5e032c05f25..a91cd2b6321 100644
--- a/gcc/realmpfr.h
+++ b/gcc/realmpfr.h
@@ -24,6 +24,26 @@
 #include <mpfr.h>
 #include <mpc.h>
 
+class auto_mpfr
+{
+public:
+  auto_mpfr () { mpfr_init (m_mpfr); }
+  explicit auto_mpfr (mpfr_prec_t prec) { mpfr_init2 (m_mpfr, prec); }
+  ~auto_mpfr () { mpfr_clear (m_mpfr); }
+
+  operator mpfr_t& () { return m_mpfr; }
+
+  auto_mpfr (const auto_mpfr &) = delete;
+  auto_mpfr &operator=(const auto_mpfr &) = delete;
+
+  friend void mpfr_clear (auto_mpfr&) = delete;
+  friend void mpfr_init (auto_mpfr&) = delete;
+  friend void mpfr_init2 (auto_mpfr&, mpfr_prec_t) = delete;
+
+private:
+  mpfr_t m_mpfr;
+};
+
 /* Convert between MPFR and REAL_VALUE_TYPE.  The caller is
    responsible for initializing and clearing the MPFR parameter.  */
 
diff --git a/gcc/system.h b/gcc/system.h
index 64cd5a49258..b16c384df6d 100644
--- a/gcc/system.h
+++ b/gcc/system.h
@@ -701,6 +701,24 @@ extern int vsnprintf (char *, size_t, const char *, va_list);
 /* Do not introduce a gmp.h dependency on the build system.  */
 #ifndef GENERATOR_FILE
 #include <gmp.h>
+
+class auto_mpz
+{
+public:
+  auto_mpz () { mpz_init (m_mpz); }
+  ~auto_mpz () { mpz_clear (m_mpz); }
+
+  operator mpz_t& () { return m_mpz; }
+
+  auto_mpz (const auto_mpz &) = delete;
+  auto_mpz &operator=(const auto_mpz &) = delete;
+
+  friend void mpz_clear (auto_mpz&) = delete;
+  friend void mpz_init (auto_mpz&) = delete;
+
+private:
+  mpz_t m_mpz;
+};
 #endif
 
 /* Get libiberty declarations.  */
diff --git a/gcc/tree-ssa-loop-niter.cc b/gcc/tree-ssa-loop-niter.cc
index dc4c7a418f6..dcfba2fc7ae 100644
--- a/gcc/tree-ssa-loop-niter.cc
+++ b/gcc/tree-ssa-loop-niter.cc
@@ -722,7 +722,6 @@ bound_difference (class loop *loop, tree x, tree y, bounds *bnds)
   tree type = TREE_TYPE (x);
   tree varx, vary;
   mpz_t offx, offy;
-  mpz_t minx, maxx, miny, maxy;
   int cnt = 0;
   edge e;
   basic_block bb;
@@ -754,19 +753,12 @@ bound_difference (class loop *loop, tree x, tree y, bounds *bnds)
     {
       /* Otherwise, use the value ranges to determine the initial
 	 estimates on below and up.  */
-      mpz_init (minx);
-      mpz_init (maxx);
-      mpz_init (miny);
-      mpz_init (maxy);
+      auto_mpz minx, maxx, miny, maxy;
       determine_value_range (loop, type, varx, offx, minx, maxx);
       determine_value_range (loop, type, vary, offy, miny, maxy);
 
       mpz_sub (bnds->below, minx, maxy);
       mpz_sub (bnds->up, maxx, miny);
-      mpz_clear (minx);
-      mpz_clear (maxx);
-      mpz_clear (miny);
-      mpz_clear (maxy);
     }
 
   /* If both X and Y are constants, we cannot get any more precise.  */
-- 
2.35.3