From ab91c10792cd3a1ba1495aa30a34ca17b043bafb Mon Sep 17 00:00:00 2001 From: Richard Biener Date: Fri, 1 Apr 2022 11:30:00 +0200 Subject: [PATCH] tree-optimization/100810 - avoid undefs in IVOPT rewrites The following attempts to avoid IVOPTs rewriting uses using IV candidates that involve undefined behavior by using uninitialized SSA names. First we restrict the set of candidates we produce for such IVs to the original ones and mark them as not important. Second we try to only allow expressing uses with such IV if they originally use them. That is to avoid rewriting all such uses in terms of other IVs. Since cand->iv and use->iv seem to never exactly match up we resort to comparing the IV bases. The approach ends up similar to the one posted by Roger at https://gcc.gnu.org/pipermail/gcc-patches/2021-August/578441.html but it marks IV candidates rather than use groups and the cases we allow in determine_group_iv_cost_generic are slightly different. 2022-01-04 Richard Biener PR tree-optimization/100810 * tree-ssa-loop-ivopts.cc (struct iv_cand): Add involves_undefs flag. (find_ssa_undef): New function. (add_candidate_1): Avoid adding derived candidates with undefined SSA names and mark the original ones. (determine_group_iv_cost_generic): Reject rewriting uses with a different IV when that involves undefined SSA names. * gcc.dg/torture/pr100810.c: New testcase. * gcc.dg/torture/pr105337.c: Likewise. --- gcc/testsuite/gcc.dg/torture/pr100810.c | 34 +++++++++++++++++++++++++++++++++ gcc/testsuite/gcc.dg/torture/pr105337.c | 31 ++++++++++++++++++++++++++++++ gcc/tree-ssa-loop-ivopts.cc | 31 ++++++++++++++++++++++++++++++ 3 files changed, 96 insertions(+) create mode 100644 gcc/testsuite/gcc.dg/torture/pr100810.c create mode 100644 gcc/testsuite/gcc.dg/torture/pr105337.c diff --git a/gcc/testsuite/gcc.dg/torture/pr100810.c b/gcc/testsuite/gcc.dg/torture/pr100810.c new file mode 100644 index 0000000..63566f5 --- /dev/null +++ b/gcc/testsuite/gcc.dg/torture/pr100810.c @@ -0,0 +1,34 @@ +/* { dg-do run } */ + +int a, b = 1, c = 1, e, f = 1, g, h, j; +volatile int d; +static void k() +{ + int i; + h = b; + if (c && a >= 0) { + while (a) { + i++; + h--; + } + if (g) + for (h = 0; h < 2; h++) + ; + if (!b) + i &&d; + } +} +static void l() +{ + for (; j < 1; j++) + if (!e && c && f) + k(); +} +int main() +{ + if (f) + l(); + if (h != 1) + __builtin_abort(); + return 0; +} diff --git a/gcc/testsuite/gcc.dg/torture/pr105337.c b/gcc/testsuite/gcc.dg/torture/pr105337.c new file mode 100644 index 0000000..4a0bdf03 --- /dev/null +++ b/gcc/testsuite/gcc.dg/torture/pr105337.c @@ -0,0 +1,31 @@ +/* { dg-do run } */ + +__attribute__((noipa)) void +bar (int x) +{ + (void) x; +} + +int a; + +int +foo (void) +{ + int b, c; + for (b = 0; b < 3; b++) + { + if (!a) + break; + c--; + bar (c); + } + return b; +} + +int +main () +{ + if (foo ()) + __builtin_abort (); + return 0; +} diff --git a/gcc/tree-ssa-loop-ivopts.cc b/gcc/tree-ssa-loop-ivopts.cc index 581f92b..81b536f 100644 --- a/gcc/tree-ssa-loop-ivopts.cc +++ b/gcc/tree-ssa-loop-ivopts.cc @@ -452,6 +452,7 @@ struct iv_cand unsigned id; /* The number of the candidate. */ bool important; /* Whether this is an "important" candidate, i.e. such that it should be considered by all uses. */ + bool involves_undefs; /* Whether the IV involves undefined values. */ ENUM_BITFIELD(iv_position) pos : 8; /* Where it is computed. */ gimple *incremented_at;/* For original biv, the statement where it is incremented. */ @@ -3070,6 +3071,19 @@ get_loop_invariant_expr (struct ivopts_data *data, tree inv_expr) return *slot; } +/* Find the first undefined SSA name in *TP. */ + +static tree +find_ssa_undef (tree *tp, int *walk_subtrees, void *) +{ + if (TREE_CODE (*tp) == SSA_NAME + && ssa_undefined_value_p (*tp, false)) + return *tp; + if (!EXPR_P (*tp)) + *walk_subtrees = 0; + return NULL; +} + /* Adds a candidate BASE + STEP * i. Important field is set to IMPORTANT and position to POS. If USE is not NULL, the candidate is set as related to it. If both BASE and STEP are NULL, we add a pseudocandidate for the @@ -3097,6 +3111,17 @@ add_candidate_1 (struct ivopts_data *data, tree base, tree step, bool important, if (flag_keep_gc_roots_live && POINTER_TYPE_P (TREE_TYPE (base))) return NULL; + /* If BASE contains undefined SSA names make sure we only record + the original IV. */ + bool involves_undefs = false; + if (walk_tree (&base, find_ssa_undef, NULL, NULL)) + { + if (pos != IP_ORIGINAL) + return NULL; + important = false; + involves_undefs = true; + } + /* For non-original variables, make sure their values are computed in a type that does not invoke undefined behavior on overflows (since in general, we cannot prove that these induction variables are non-wrapping). */ @@ -3145,6 +3170,7 @@ add_candidate_1 (struct ivopts_data *data, tree base, tree step, bool important, cand->var_after = cand->var_before; } cand->important = important; + cand->involves_undefs = involves_undefs; cand->incremented_at = incremented_at; cand->doloop_p = doloop; data->vcands.safe_push (cand); @@ -4958,6 +4984,11 @@ determine_group_iv_cost_generic (struct ivopts_data *data, the candidate. */ if (cand->pos == IP_ORIGINAL && cand->incremented_at == use->stmt) cost = no_cost; + /* If the IV candidate involves undefined SSA values and is not the + same IV as on the USE avoid using that candidate here. */ + else if (cand->involves_undefs + && (!use->iv || !operand_equal_p (cand->iv->base, use->iv->base, 0))) + return false; else cost = get_computation_cost (data, use, cand, false, &inv_vars, NULL, &inv_expr); -- 2.7.4