On Mon, 3 May 2021, Jan Hubicka wrote: > > note that if you wrap foo () into another noinline > > wrap_foo () { foo (); return 1; } function then we need to make > > sure to not DCE this call either even though it only throws > > externally. Now the question is whether this testcase is valid > > (it should not abort). The documentation of 'pure' must be read > > as that 'pure' is not valid for 'foo' since throwing an exception > > is obviously an observable effect on the state of the program > > (in particular for the testcase at hand). But for example > > IPA pure const does not cause us to infer nothrow on pure > > declared functions and the C++ program > > > > extern int __attribute__((pure)) foo(); > > int bar() > > { > > try > > { > > return foo (); > > } > > catch (...) > > { > > return -1; > > } > > } > > > > is compiled with full EH in place. (clang elides all of it, btw) > > > > The set of changes below do not succeed in it passing but at least > > the throwing call prevails but somehow EH info is hosed and you'll > > get > > > > > ./pr100382.exe > > terminate called without an active exception > > Aborted (core dumped) > > > > So - what is it? Are pure functions allowed to throw or not? > > I was one adding pure functions and it was really intended to be same > thing as const+reading memory. So does const function throw or not? > Internally we definitly want to make this separate - with symbol > summaries it is now reasonably easy to do. I was thinking of doing > similar summary as modref handles to pass down separate info tracked by > pure-const patch rather than trying to re-synthetize it to rather random > attributes we have now...
Yes, we handle 'const' as throwing (well, we don't optimize it as not throwing...). But since 'const' is a subset of 'pure' functions if pure functions cannot throw then const functions can not either. extern int __attribute__((const)) foo(); int bar() { try { return foo (); } catch (...) { return -1; } } has EH emitted as well. Richard. > Honza > > > > 2021-05-03 Richard Biener <rguent...@suse.de> > > > > * calls.c (expand_call): Preserve possibly throwing calls. > > * cfgexpand.c (expand_call_stmt): When a call can throw signal > > RTL expansion there are side-effects. > > * tree-ssa-dce.c (mark_stmt_if_obviously_necessary): Simplify. > > * tree-ssa-dse.c (pass_dse::execute): Preserve exceptions unless > > -fdelete-dead-exceptions. > > > > * g++.dg/tree-ssa/pr100382.C: New testcase. > > --- > > gcc/calls.c | 1 + > > gcc/cfgexpand.c | 5 ++++- > > gcc/testsuite/g++.dg/tree-ssa/pr100382.C | 25 ++++++++++++++++++++++++ > > gcc/tree-ssa-dce.c | 21 +++----------------- > > gcc/tree-ssa-dse.c | 3 ++- > > 5 files changed, 35 insertions(+), 20 deletions(-) > > create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr100382.C > > > > diff --git a/gcc/calls.c b/gcc/calls.c > > index 883d08ba5f2..f3da1839dc5 100644 > > --- a/gcc/calls.c > > +++ b/gcc/calls.c > > @@ -3808,6 +3808,7 @@ expand_call (tree exp, rtx target, int ignore) > > side-effects. */ > > if ((flags & (ECF_CONST | ECF_PURE)) > > && (!(flags & ECF_LOOPING_CONST_OR_PURE)) > > + && (flags & ECF_NOTHROW) > > && (ignore || target == const0_rtx > > || TYPE_MODE (rettype) == VOIDmode)) > > { > > diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c > > index a6b48d3e48f..556a0b22ed6 100644 > > --- a/gcc/cfgexpand.c > > +++ b/gcc/cfgexpand.c > > @@ -2795,7 +2795,10 @@ expand_call_stmt (gcall *stmt) > > CALL_EXPR_ARG (exp, i) = arg; > > } > > > > - if (gimple_has_side_effects (stmt)) > > + if (gimple_has_side_effects (stmt) > > + /* ??? Downstream in expand_expr_real_1 we assume that expressions > > + w/o side-effects do not throw so work around this here. */ > > + || stmt_could_throw_p (cfun, stmt)) > > TREE_SIDE_EFFECTS (exp) = 1; > > > > if (gimple_call_nothrow_p (stmt)) > > diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr100382.C > > b/gcc/testsuite/g++.dg/tree-ssa/pr100382.C > > new file mode 100644 > > index 00000000000..b9948d3034a > > --- /dev/null > > +++ b/gcc/testsuite/g++.dg/tree-ssa/pr100382.C > > @@ -0,0 +1,25 @@ > > +// { dg-do run } > > +// { dg-options "-O2" } > > + > > +int x, y; > > +int __attribute__((pure,noinline)) foo () { if (x) throw; return y; } > > + > > +int __attribute__((noinline)) bar() > > +{ > > + int a[2]; > > + x = 1; > > + try { > > + int res = foo (); > > + a[0] = res; > > + } catch (...) { > > + return 0; > > + } > > + return 1; > > +} > > + > > +int main() > > +{ > > + if (bar ()) > > + __builtin_abort (); > > + return 0; > > +} > > diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c > > index 096cfc8721d..ff0389af36f 100644 > > --- a/gcc/tree-ssa-dce.c > > +++ b/gcc/tree-ssa-dce.c > > @@ -250,14 +250,6 @@ mark_stmt_if_obviously_necessary (gimple *stmt, bool > > aggressive) > > && DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee)) > > return; > > > > - /* Most, but not all function calls are required. Function calls that > > - produce no result and have no side effects (i.e. const pure > > - functions) are unnecessary. */ > > - if (gimple_has_side_effects (stmt)) > > - { > > - mark_stmt_necessary (stmt, true); > > - return; > > - } > > /* IFN_GOACC_LOOP calls are necessary in that they are used to > > represent parameter (i.e. step, bound) of a lowered OpenACC > > partitioned loop. But this kind of partitioned loop might not > > @@ -269,8 +261,6 @@ mark_stmt_if_obviously_necessary (gimple *stmt, bool > > aggressive) > > mark_stmt_necessary (stmt, true); > > return; > > } > > - if (!gimple_call_lhs (stmt)) > > - return; > > break; > > } > > > > @@ -312,19 +302,14 @@ mark_stmt_if_obviously_necessary (gimple *stmt, bool > > aggressive) > > /* If the statement has volatile operands, it needs to be preserved. > > Same for statements that can alter control flow in unpredictable > > ways. */ > > - if (gimple_has_volatile_ops (stmt) || is_ctrl_altering_stmt (stmt)) > > - { > > - mark_stmt_necessary (stmt, true); > > - return; > > - } > > - > > - if (stmt_may_clobber_global_p (stmt)) > > + if (gimple_has_side_effects (stmt) || is_ctrl_altering_stmt (stmt)) > > { > > mark_stmt_necessary (stmt, true); > > return; > > } > > > > - if (gimple_vdef (stmt) && keep_all_vdefs_p ()) > > + if ((gimple_vdef (stmt) && keep_all_vdefs_p ()) > > + || stmt_may_clobber_global_p (stmt)) > > { > > mark_stmt_necessary (stmt, true); > > return; > > diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c > > index dfa6d314727..386667b9f7f 100644 > > --- a/gcc/tree-ssa-dse.c > > +++ b/gcc/tree-ssa-dse.c > > @@ -1219,7 +1219,8 @@ pass_dse::execute (function *fun) > > dead SSA defs. */ > > if (has_zero_uses (DEF_FROM_PTR (def_p)) > > && !gimple_has_side_effects (stmt) > > - && !stmt_unremovable_because_of_non_call_eh_p (cfun, stmt)) > > + && (!stmt_could_throw_p (fun, stmt) > > + || fun->can_delete_dead_exceptions)) > > { > > if (dump_file && (dump_flags & TDF_DETAILS)) > > { > > -- > > 2.26.2 > -- Richard Biener <rguent...@suse.de> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)