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From: Richard Biener <rguenth@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r13-3810] tree-optimization/107389 - honor __builtin_assume_alignment at -O0 Date: Tue, 8 Nov 2022 15:39:55 +0000 (GMT) [thread overview] Message-ID: <20221108153955.313D03858D35@sourceware.org> (raw) https://gcc.gnu.org/g:7899582a059a9d8c25bfff305cd236d219dc4f20 commit r13-3810-g7899582a059a9d8c25bfff305cd236d219dc4f20 Author: Richard Biener <rguenther@suse.de> Date: Tue Nov 8 13:49:16 2022 +0100 tree-optimization/107389 - honor __builtin_assume_alignment at -O0 The following makes sure to set alignment information on the LHS of __builtin_assume_alignment calls even when not optimizing so uses as arguments to builtin functions like memcpy or __atomic_load_n can be reflected at RTL expansion time. PR tree-optimization/107389 * gimple-low.cc (lower_builtin_assume_aligned): New. (lower_stmt): Call it. * gcc.dg/pr107389.c: New testcase. Diff: --- gcc/gimple-low.cc | 41 +++++++++++++++++++++++++++++++++++++++++ gcc/testsuite/gcc.dg/pr107389.c | 13 +++++++++++++ 2 files changed, 54 insertions(+) diff --git a/gcc/gimple-low.cc b/gcc/gimple-low.cc index 512aa9feada..53df2e7b212 100644 --- a/gcc/gimple-low.cc +++ b/gcc/gimple-low.cc @@ -84,6 +84,7 @@ static void lower_try_catch (gimple_stmt_iterator *, struct lower_data *); static void lower_gimple_return (gimple_stmt_iterator *, struct lower_data *); static void lower_builtin_setjmp (gimple_stmt_iterator *); static void lower_builtin_posix_memalign (gimple_stmt_iterator *); +static void lower_builtin_assume_aligned (gimple_stmt_iterator *); /* Lower the body of current_function_decl from High GIMPLE into Low @@ -768,6 +769,14 @@ lower_stmt (gimple_stmt_iterator *gsi, struct lower_data *data) lower_builtin_posix_memalign (gsi); return; } + else if (DECL_FUNCTION_CODE (decl) == BUILT_IN_ASSUME_ALIGNED + && !optimize) + { + lower_builtin_assume_aligned (gsi); + data->cannot_fallthru = false; + gsi_next (gsi); + return; + } } if (decl && (flags_from_decl_or_type (decl) & ECF_NORETURN)) @@ -1310,6 +1319,38 @@ lower_builtin_posix_memalign (gimple_stmt_iterator *gsi) gsi_insert_after (gsi, stmt, GSI_NEW_STMT); gsi_insert_after (gsi, gimple_build_label (noalign_label), GSI_NEW_STMT); } + +/* Lower calls to __builtin_assume_aligned when not optimizing. */ + +static void +lower_builtin_assume_aligned (gimple_stmt_iterator *gsi) +{ + gcall *call = as_a <gcall *> (gsi_stmt (*gsi)); + + tree lhs = gimple_call_lhs (call); + if (!lhs || !POINTER_TYPE_P (TREE_TYPE (lhs)) || TREE_CODE (lhs) != SSA_NAME) + return; + + tree align = gimple_call_arg (call, 1); + tree misalign = (gimple_call_num_args (call) > 2 + ? gimple_call_arg (call, 2) : NULL_TREE); + if (!tree_fits_uhwi_p (align) + || (misalign && !tree_fits_uhwi_p (misalign))) + return; + + unsigned aligni = TREE_INT_CST_LOW (align); + unsigned misaligni = misalign ? TREE_INT_CST_LOW (misalign) : 0; + if (aligni <= 1 + || (aligni & (aligni - 1)) != 0 + || (misaligni & ~(aligni - 1)) != 0) + return; + + /* For lowering we simply transfer alignment information to the + result and leave the call otherwise unchanged, it will be elided + at RTL expansion time. */ + ptr_info_def *pi = get_ptr_info (lhs); + set_ptr_info_alignment (pi, aligni, misaligni); +} \f /* Record the variables in VARS into function FN. */ diff --git a/gcc/testsuite/gcc.dg/pr107389.c b/gcc/testsuite/gcc.dg/pr107389.c new file mode 100644 index 00000000000..deb63380704 --- /dev/null +++ b/gcc/testsuite/gcc.dg/pr107389.c @@ -0,0 +1,13 @@ +/* { dg-do compile } */ +/* { dg-options "-fdump-tree-optimized-alias" } */ + +unsigned foo (void *p) +{ + unsigned i; + __builtin_memcpy (&i, __builtin_assume_aligned (p, 4), sizeof (unsigned)); + return i; +} + +/* Even when not optimizing we should have alignment info on the temporary + feeding the memcpy. */ +/* { dg-final { scan-tree-dump "ALIGN = 4" "optimized" } } */
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