From f6c168f8c06047bfaa3005e570126831b8855dcc Mon Sep 17 00:00:00 2001 From: Martin Jambor Date: Wed, 19 Oct 2022 14:43:04 +0200 Subject: [PATCH] SRA: Limit replacement creation for accesses propagated from LHSs PR 107206 is fallout from the fix to PR 92706 where we started propagating accesses across assignments also from LHS to RHS of assignments so that we would not do harmful total scalarization of the aggregates on the RHS. But this can lead to new scalarization of these aggregates and in the testcase of PR 107206 these can appear in superfluous uses of un-initialized values and spurious warnings. Fixed by making sure the the accesses created by propagation in this direction are only used as a basis for replacements when the structure would be totally scalarized anyway. gcc/ChangeLog: 2022-10-18 Martin Jambor PR tree-optimization/107206 * tree-sra.cc (struct access): New field grp_result_of_prop_from_lhs. (analyze_access_subtree): Do not create replacements for accesses with this flag when not toally scalarizing. (propagate_subaccesses_from_lhs): Set the new flag. gcc/testsuite/ChangeLog: 2022-10-18 Martin Jambor PR tree-optimization/107206 * g++.dg/tree-ssa/pr107206.C: New test. --- gcc/testsuite/g++.dg/tree-ssa/pr107206.C | 27 +++++++++++++++++++++++++++ gcc/tree-sra.cc | 7 +++++++ 2 files changed, 34 insertions(+) create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr107206.C diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr107206.C b/gcc/testsuite/g++.dg/tree-ssa/pr107206.C new file mode 100644 index 0000000..34810ad --- /dev/null +++ b/gcc/testsuite/g++.dg/tree-ssa/pr107206.C @@ -0,0 +1,27 @@ +// { dg-do compile } +// { dg-require-effective-target c++17 } +// { dg-options "-O -Wuninitialized" } + +#include +struct X { + X() = default; + X(X const& r) : i(r.i) {} + int i; +}; +struct Y { + Y() : x() {} + X x; + std::optional o; +}; +struct Z { + Y y; + explicit Z(Y y) : y(y) {} +}; +void f(Y const&); +void test() { + Y const y; + Z z(y); + z.y.o = 1; + auto const w = z; + f(w.y); +} diff --git a/gcc/tree-sra.cc b/gcc/tree-sra.cc index 1a3e12f..6cbeddf 100644 --- a/gcc/tree-sra.cc +++ b/gcc/tree-sra.cc @@ -260,6 +260,9 @@ struct access /* Should TREE_NO_WARNING of a replacement be set? */ unsigned grp_no_warning : 1; + + /* Result of propagation accross link from LHS to RHS. */ + unsigned grp_result_of_prop_from_lhs : 1; }; typedef struct access *access_p; @@ -2532,6 +2535,9 @@ analyze_access_subtree (struct access *root, struct access *parent, if (allow_replacements && expr_with_var_bounded_array_refs_p (root->expr)) allow_replacements = false; + if (!totally && root->grp_result_of_prop_from_lhs) + allow_replacements = false; + for (child = root->first_child; child; child = child->next_sibling) { hole |= covered_to < child->offset; @@ -2959,6 +2965,7 @@ propagate_subaccesses_from_lhs (struct access *lacc, struct access *racc) struct access *new_acc = create_artificial_child_access (racc, lchild, norm_offset, true, false); + new_acc->grp_result_of_prop_from_lhs = 1; propagate_subaccesses_from_lhs (lchild, new_acc); } else -- 2.7.4