https://gcc.gnu.org/g:8590b32deac05e6eb368b72bd353749134120a1f
commit r16-4637-g8590b32deac05e6eb368b72bd353749134120a1f Author: Andrew Pinski <[email protected]> Date: Fri Oct 24 17:13:26 2025 -0700 forwprop: Fix copy prop for alignment after the final folding [PR122086] After r16-4081-g966cdec2b2 which added folding of __builtin_assume_aligned, forwprop would propagate pointers that lower alignment replacing ones with greater alignment. This causes us to lose alignment information that __builtin_assume_aligned provided to expand. Normally this just loses some optimizations except in the s390 case where the alignment is specifically checked and was for inlining of the atomics; without this patch an infininite loop would happen. Note this was previously broken for -Og before r16-4081-g966cdec2b2. This fixes -Og case as forwprop is used instead of copyprop. This moves the testcase for pr107389.c to torture to get a generic testcase. pr107389.c was originally for -O0 case but we should test for other optimization levels so this is not lost again. align-5.c is xfailed because __builtin_assume_aligned is not instrumented for ubsan alignment and ubsan check to see pointer is aligned before emitting a check for the load (based on the known alignment in compiling). See PR 122038 too. I had mentioned this issue previously in r16-4081-g966cdec2b2 too. PR middle-end/107389 PR tree-optimization/122086 gcc/ChangeLog: * tree-ssa-forwprop.cc (forwprop_may_propagate_copy): New function. (pass_forwprop::execute): Use forwprop_may_propagate_copy instead of may_propagate_copy. gcc/testsuite/ChangeLog: * gcc.dg/pr107389.c: Move to... * gcc.dg/torture/pr107389.c: ...here. Skip for lto. Use dg-additional-options rather than dg-options. * c-c++-common/ubsan/align-5.c: xfail. Signed-off-by: Andrew Pinski <[email protected]> Diff: --- gcc/testsuite/c-c++-common/ubsan/align-5.c | 4 +++- gcc/testsuite/gcc.dg/{ => torture}/pr107389.c | 3 ++- gcc/tree-ssa-forwprop.cc | 33 +++++++++++++++++++++++---- 3 files changed, 34 insertions(+), 6 deletions(-) diff --git a/gcc/testsuite/c-c++-common/ubsan/align-5.c b/gcc/testsuite/c-c++-common/ubsan/align-5.c index 484790134a66..6d2ac26612bb 100644 --- a/gcc/testsuite/c-c++-common/ubsan/align-5.c +++ b/gcc/testsuite/c-c++-common/ubsan/align-5.c @@ -11,4 +11,6 @@ foo (char *p) return *q; } -/* { dg-final { scan-assembler "__ubsan_handle" } } */ +/* xfail, see PR 122038 as __builtin_assume_aligned should be instrumented instead + of only the load. */ +/* { dg-final { scan-assembler "__ubsan_handle" { xfail *-*-* } } } */ diff --git a/gcc/testsuite/gcc.dg/pr107389.c b/gcc/testsuite/gcc.dg/torture/pr107389.c similarity index 73% rename from gcc/testsuite/gcc.dg/pr107389.c rename to gcc/testsuite/gcc.dg/torture/pr107389.c index deb633807044..23c2776ab736 100644 --- a/gcc/testsuite/gcc.dg/pr107389.c +++ b/gcc/testsuite/gcc.dg/torture/pr107389.c @@ -1,5 +1,6 @@ /* { dg-do compile } */ -/* { dg-options "-fdump-tree-optimized-alias" } */ +/* { dg-skip-if "" { *-*-* } { "-flto" } { "" } } */ +/* { dg-additional-options "-fdump-tree-optimized-alias" } */ unsigned foo (void *p) { diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc index 68e80baa46c0..79ac25f7ed57 100644 --- a/gcc/tree-ssa-forwprop.cc +++ b/gcc/tree-ssa-forwprop.cc @@ -216,6 +216,31 @@ static bitmap to_purge; /* Const-and-copy lattice. */ static vec<tree> lattice; +/* forwprop_may_propagate_copy is like may_propagate_copy except + after the final folding, don't allow propagating of pointer ORIG + that have a lower alignment than the DEST name. + This is to prevent losing alignment information from + __builtin_assume_aligned for expand (See also PR 122086). */ +static bool +forwprop_may_propagate_copy (tree dest, tree orig, + bool dest_not_abnormal_phi_edge_p = false) +{ + if (!may_propagate_copy (dest, orig, dest_not_abnormal_phi_edge_p)) + return false; + + /* Only check alignment for the final folding. */ + if (!(cfun->curr_properties & PROP_last_full_fold)) + return true; + + /* Alignment only matters for pointer types. */ + if (!POINTER_TYPE_P (TREE_TYPE (dest)) || !POINTER_TYPE_P (TREE_TYPE (orig))) + return true; + + unsigned aligndest = get_pointer_alignment (dest); + unsigned alignorig = get_pointer_alignment (orig); + return aligndest <= alignorig; +} + /* Set the lattice entry for NAME to VAL. */ static void fwprop_set_lattice_val (tree name, tree val) @@ -5177,7 +5202,7 @@ pass_forwprop::execute (function *fun) } if (all_same) { - if (may_propagate_copy (res, first)) + if (forwprop_may_propagate_copy (res, first)) to_remove_defs.safe_push (SSA_NAME_VERSION (res)); fwprop_set_lattice_val (res, first); } @@ -5532,7 +5557,7 @@ pass_forwprop::execute (function *fun) { if (!is_gimple_debug (stmt)) bitmap_set_bit (simple_dce_worklist, SSA_NAME_VERSION (use)); - if (may_propagate_copy (use, val)) + if (forwprop_may_propagate_copy (use, val)) { propagate_value (usep, val); substituted_p = true; @@ -5695,7 +5720,7 @@ pass_forwprop::execute (function *fun) /* If we can propagate the lattice-value mark the stmt for removal. */ if (val != lhs - && may_propagate_copy (lhs, val)) + && forwprop_may_propagate_copy (lhs, val)) to_remove_defs.safe_push (SSA_NAME_VERSION (lhs)); fwprop_set_lattice_val (lhs, val); } @@ -5717,7 +5742,7 @@ pass_forwprop::execute (function *fun) continue; tree val = fwprop_ssa_val (arg); if (val != arg - && may_propagate_copy (arg, val, !(e->flags & EDGE_ABNORMAL))) + && forwprop_may_propagate_copy (arg, val, !(e->flags & EDGE_ABNORMAL))) propagate_value (use_p, val); }
