7247 – [3.2 regression] copy constructor missing when inlining enabled for i386 (original) (raw)

| A copy constructor for a class is not called at the bottom of a complex expression involving many small inlined functions. The class in question is "double_zero", defined at line 121. It does not matter whether the constructor is defined explicitly or by compiler itself. The place its copy contructor ought to be called is the constructor of "modified_container_base" (line 91), instantiated from "TransformedContainer" (line 156), instantiated in its turn from "IncidenceMatrix" (line 293). Sorry for a lengthy example; if I would simplify the code a bit further, the bug would disappear. The original program had over 60K lines. The bug disappears when inlining is disabled, but also when the function "attach_operation" (line 165) is made more fat by inserting "dump_op(op);" at its beginning. Surprisingly, the whole expression remains inlined, but the resulting code is suddenly correct! On a UltraSPARC platform (Solaris 8), this bug does not occur at all, in any setting. gcc 3.0.4 seems to be free of this bug on both platforms. Release: 3.1 Environment: Reading specs from /usr/site-local/experimental/lib/gcc-lib/i686-pc-linux-gnu/3.1/specs Configured with: ../gcc-3.1/configure --prefix=/usr/site-local/experimental --with-local-prefix=/usr/site-local --with-gxx-include-dir=/usr/site-local/share/include/g++ --enable-shared --enable-libgcj --enable-languages=c++,java --with-cpu=athlon Thread model: single gcc version 3.1 How-To-Repeat: compile the attached program with -O3 and run it. If the generated code is correct, both lines printed will contain the same number, 1e-5. Comment 1 Nathan Sidwell 2002-07-09 12:07:05 UTC State-Changed-From-To: open->feedback State-Changed-Why: If I understand you correctly, you are complaining that a copy ctor call is being optimized away. This is allowed, under [12.8]/15, even if the copy ctor has side-effects Comment 2 gawrilow 2002-07-10 11:07:57 UTC From: Ewgenij Gawrilow <gawrilow@math.TU-Berlin.DE> To: nathan@gcc.gnu.org Cc: gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org, gcc-prs@gcc.gnu.org Subject: Re: optimization/7247: copy constructor missing when inlining enabled for i386 Date: Wed, 10 Jul 2002 11:07:57 +0200 >>>>> "nathan" == nathan <nathan@gcc.gnu.org> writes: nathan> Synopsis: copy constructor missing when inlining enabled nathan> for i386 nathan> If I understand you correctly, you are nathan> complaining that a copy ctor call is being optimized away. nathan> This is allowed, under [12.8]/15, even if the copy ctor nathan> has side-effects The class whose construction fails is defined in my test case as follows: struct double_zero { const double epsilon; double_zero(const double& epsilon_arg=1e-8) : epsilon(epsilon_arg) { } }; One would expect from a copy constructor, especially from the implicit one, that it would copy the value of the instance variable "epsilon". I don't think this could fall under the definition of a side effect. Alternatively, if optimization according to the clause [12.8]/15 comes into effect here, as you mean, then it is the constructor double_zero(const double&) that is being forgotten. At any rate, the "epsilon" variable contains garbage after the construction, as shows up in the debugging output. Encouraged by such a quick response, I hope for a similarly quick fix :-) With best regards, Ewgenij Gawrilow Comment 3 Jason Merrill 2002-07-11 22:02:12 UTC From: Jason Merrill <jason@redhat.com> To: "H. J. Lu" <hjl@lucon.org> Cc: gawrilow@math.tu-berlin.de, gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org Subject: Re: optimization/7247: copy constructor missing when inlining enabled for i386 Date: Thu, 11 Jul 2002 22:02:12 +0100 >>>>> "H" == H J Lu <hjl@lucon.org> writes: > Jason, it looks like your patch doesn't catch this one. No, as the bug isn't related to the NRVO; this testcase doesn't have any returns which would be affected. Rather, it seems to be a dependency tracking bug. I can reproduce the bug by adding 'inline' to the definition of incidence_matrix and compiling with -O -fschedule-insns2. Without -fschedule-insns2, the code leading up to the dump_op calls looks like movl -96(%ebp), %eax movl -92(%ebp), %edx movl %eax, -52(%ebp) movl %edx, -48(%ebp) leal -96(%ebp), %eax movl %eax, (%esp) call pm::dump_op(pm::double_zero const&) leal -52(%ebp), %eax movl %eax, (%esp) call pm::dump_op(pm::double_zero const&) so the epsilon value is properly copied before it is dumped. But with scheduling, it looks like movl -96(%ebp), %eax movl %eax, -52(%ebp) leal -96(%ebp), %eax movl %eax, (%esp) call pm::dump_op(pm::double_zero const&) leal -52(%ebp), %eax movl %eax, (%esp) call pm::dump_op(pm::double_zero const&) Which suggests that the scheduler incorrectly decides that the second word wasn't used by the call and optimizes away the copy. This bug, or a similar one, seems still to be present in the trunk, though to see it you also need to move the definition of the double_zero constructor outside the class, so it is not inlined. Jason Comment 4 Volker Reichelt 2002-12-19 06:19:45 UTC State-Changed-From-To: feedback->analyzed State-Changed-Why: Confirmed (just for the record). Here's a reduced testcase that fails on the 3.2 branch. gcc 3.0.x, 3.3 and mainline do not seem to be affected. --------------------------------snip here--------------------------------- extern "C" { extern int printf (const char *, ...) throw (); } struct A { const double d; A() : d(1e-4) {} void dump () const { printf("%e\n", d); } }; struct B { A a; int i; B(const A& arg) : a(arg) { arg.dump(); a.dump();} }; struct C : B { C(const A& arg) : B(arg) {} }; struct X { int i, j, k; X() : j(0) {} }; struct Y { template Y(int, const T&) {} }; inline int foo() { X x; return 0; } int main() { Y y(foo(), C(A())); return 0; } --------------------------------snip here--------------------------------- Just compile with "-O2" or "-O -fschedule-insns2" (on i686-pc-linux-gnu) to get the wrong result 1.000000e-04 1.948841e-314 instead of 1.000000e-04 1.000000e-04 Regards, Volker Comment 6 Joe Buck 2003-04-25 19:51:03 UTC State-Changed-From-To: analyzed->closed State-Changed-Why: Fixed for the next release (3.3). | | | 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