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From: Alexandre Oliva <aoliva@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc(refs/users/aoliva/heads/testme)] harden-conditionals: detach values before compares Date: Thu, 27 Apr 2023 07:07:51 +0000 (GMT) [thread overview] Message-ID: <20230427070751.542D13858D20@sourceware.org> (raw) https://gcc.gnu.org/g:dedcaad4ce197947fb4e70a71cafdd00780d2036 commit dedcaad4ce197947fb4e70a71cafdd00780d2036 Author: Alexandre Oliva <oliva@adacore.com> Date: Thu Apr 27 02:43:48 2023 -0300 harden-conditionals: detach values before compares The optimization barriers inserted after compares enable GCC to derive information about the values from e.g. the taken paths, or the absence of exceptions. Move them before the original compares, so that the reversed compares test copies of the original operands, without further optimizations. for gcc/ChangeLog * gimple-harden-conditionals.cc (insert_edge_check_and_trap): Move detach value calls... (pass_harden_conditional_branches::execute): ... here. (pass_harden_compares::execute): Detach values before compares. for gcc/testsuite/ChangeLog * c-c++-common/torture/harden-cond-comp.c: New. Diff: --- gcc/gimple-harden-conditionals.cc | 25 +++++++++++++--------- .../c-c++-common/torture/harden-cond-comp.c | 24 +++++++++++++++++++++ 2 files changed, 39 insertions(+), 10 deletions(-) diff --git a/gcc/gimple-harden-conditionals.cc b/gcc/gimple-harden-conditionals.cc index 78b8d5692d7..2e5a42e9e71 100644 --- a/gcc/gimple-harden-conditionals.cc +++ b/gcc/gimple-harden-conditionals.cc @@ -276,8 +276,8 @@ insert_check_and_trap (location_t loc, gimple_stmt_iterator *gsip, } /* Split edge E, and insert_check_and_trap (see above) in the - newly-created block, using detached copies of LHS's and RHS's - values (see detach_value above) for the COP compare. */ + newly-created block, using already-detached copies of LHS's and + RHS's values (see detach_value above) for the COP compare. */ static inline void insert_edge_check_and_trap (location_t loc, edge e, @@ -301,10 +301,6 @@ insert_edge_check_and_trap (location_t loc, edge e, gimple_stmt_iterator gsik = gsi_after_labels (chk); - bool same_p = (lhs == rhs); - lhs = detach_value (loc, &gsik, lhs); - rhs = same_p ? lhs : detach_value (loc, &gsik, rhs); - insert_check_and_trap (loc, &gsik, flags, cop, lhs, rhs); } @@ -366,6 +362,12 @@ pass_harden_conditional_branches::execute (function *fun) /* ??? Can we do better? */ continue; + /* Detach the values before the compares. If we do so later, + the compiler may use values inferred from the compares. */ + bool same_p = (lhs == rhs); + lhs = detach_value (loc, &gsi, lhs); + rhs = same_p ? lhs : detach_value (loc, &gsi, rhs); + insert_edge_check_and_trap (loc, EDGE_SUCC (bb, 0), cop, lhs, rhs); insert_edge_check_and_trap (loc, EDGE_SUCC (bb, 1), cop, lhs, rhs); } @@ -508,6 +510,13 @@ pass_harden_compares::execute (function *fun) tree rhs = copy_ssa_name (lhs); + /* Detach the values before the compares, so that the + compiler infers nothing from them, not even from a + throwing compare that didn't throw. */ + bool same_p = (op1 == op2); + op1 = detach_value (loc, &gsi, op1); + op2 = same_p ? op1 : detach_value (loc, &gsi, op2); + gimple_stmt_iterator gsi_split = gsi; /* Don't separate the original assignment from debug stmts that might be associated with it, and arrange to split the @@ -529,10 +538,6 @@ pass_harden_compares::execute (function *fun) gimple_bb (asgn)->index, nbb->index); } - bool same_p = (op1 == op2); - op1 = detach_value (loc, &gsi_split, op1); - op2 = same_p ? op1 : detach_value (loc, &gsi_split, op2); - gassign *asgnck = gimple_build_assign (rhs, cop, op1, op2); gimple_set_location (asgnck, loc); gsi_insert_before (&gsi_split, asgnck, GSI_SAME_STMT); diff --git a/gcc/testsuite/c-c++-common/torture/harden-cond-comp.c b/gcc/testsuite/c-c++-common/torture/harden-cond-comp.c new file mode 100644 index 00000000000..5aad890a1d3 --- /dev/null +++ b/gcc/testsuite/c-c++-common/torture/harden-cond-comp.c @@ -0,0 +1,24 @@ +/* { dg-do compile } */ +/* { dg-options "-fharden-conditional-branches -fharden-compares -fdump-tree-hardcbr -fdump-tree-hardcmp -ffat-lto-objects" } */ + +int f(int i, int j) { + if (i == 0) + return j != 0; + else + return i * j != 0; +} + +/* { dg-final { scan-tree-dump-times "Splitting edge" 2 "hardcbr" } } */ +/* { dg-final { scan-tree-dump-times "Adding reversed compare" 2 "hardcbr" } } */ +/* { dg-final { scan-tree-dump-times "__builtin_trap" 2 "hardcbr" } } */ + +/* { dg-final { scan-tree-dump-times "Splitting block" 2 "hardcmp" } } */ +/* { dg-final { scan-tree-dump-times "Adding reversed compare" 2 "hardcmp" } } */ +/* { dg-final { scan-tree-dump-times "__builtin_trap" 4 "hardcmp" } } */ + +/* Check that the optimization barrier is placed before the original compare. */ +/* { dg-final { scan-tree-dump-times {__asm__[(]"" : "=g" _[0-9]* : "0" i_[0-9]*[(]D[)][)][;][\n][ ]*if [(]i_[0-9]*[(]D[)] == 0[)]} 1 "hardcbr" } } */ +/* { dg-final { scan-tree-dump-times {if [(]_[0-9]* != 0[)]} 2 "hardcbr" } } */ + +/* { dg-final { scan-tree-dump-times {__asm__[(]"" : "=g" _[0-9]* : "0" j_[0-9]*[(]D[)][)][;][\n][ ]*_[0-9]* = j_[0-9]*[(]D[)] != 0;[\n] *_[0-9]* = _[0-9]* == 0} 1 "hardcmp" } } */ +/* { dg-final { scan-tree-dump-times {__asm__[(]"" : "=g" _[0-9]* : "0" _[0-9]*[)][;][\n][ ]*_[0-9]* = _[0-9]* != 0;[\n] *_[0-9]* = _[0-9]* == 0} 1 "hardcmp" } } */
next reply other threads:[~2023-04-27 7:07 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-04-27 7:07 Alexandre Oliva [this message] -- strict thread matches above, loose matches on Subject: below -- 2023-06-09 6:16 Alexandre Oliva 2023-06-08 10:42 Alexandre Oliva 2023-04-27 5:59 Alexandre Oliva
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