From 04eccbbe3d9a4e9d2f8f43dba8ac4cb686029fb2 Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Wed, 24 Nov 2021 09:54:44 +0100 Subject: [PATCH] bswap: Fix up symbolic merging for xor and plus [PR103376] On Mon, Nov 22, 2021 at 08:39:42AM -0000, Roger Sayle wrote: > This patch implements PR tree-optimization/103345 to merge adjacent > loads when combined with addition or bitwise xor. The current code > in gimple-ssa-store-merging.c's find_bswap_or_nop alreay handles ior, > so that all that's required is to treat PLUS_EXPR and BIT_XOR_EXPR in > the same way at BIT_IOR_EXPR. Unfortunately they aren't exactly the same. They work the same if always at least one operand (or corresponding byte in it) is known to be 0, 0 | 0 = 0 ^ 0 = 0 + 0 = 0. But for | also x | x = x for any other x, so perform_symbolic_merge has been accepting either that at least one of the bytes is 0 or that both are the same, but that is wrong for ^ and +. The following patch fixes that by passing through the code of binary operation and allowing non-zero masked1 == masked2 through only for BIT_IOR_EXPR. Thinking more about it, perhaps we could do more for BIT_XOR_EXPR. We could allow masked1 == masked2 case for it, but would need to do something different than the n->n = n1->n | n2->n; we do on all the bytes together. In particular, for masked1 == masked2 if masked1 != 0 (well, for 0 both variants are the same) and masked1 != 0xff we would need to clear corresponding n->n byte instead of setting it to the input as x ^ x = 0 (but if we don't know what x and y are, the result is also don't know). Now, for plus it is much harder, because not only for non-zero operands we don't know what the result is, but it can modify upper bytes as well. So perhaps only if current's byte masked1 && masked2 set the resulting byte to 0xff (unknown) iff the byte above it is 0 and 0, and set that resulting byte to 0xff too. Also, even for | we could instead of return NULL just set the resulting byte to 0xff if it is different, perhaps it will be masked off later on. 2021-11-24 Jakub Jelinek PR tree-optimization/103376 * gimple-ssa-store-merging.c (perform_symbolic_merge): Add CODE argument. If CODE is not BIT_IOR_EXPR, ensure that one of masked1 or masked2 is 0. (find_bswap_or_nop_1, find_bswap_or_nop, imm_store_chain_info::try_coalesce_bswap): Adjust perform_symbolic_merge callers. * gcc.c-torture/execute/pr103376.c: New test. --- gcc/gimple-ssa-store-merging.c | 20 ++++++++----- .../gcc.c-torture/execute/pr103376.c | 29 +++++++++++++++++++ 2 files changed, 41 insertions(+), 8 deletions(-) create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr103376.c diff --git a/gcc/gimple-ssa-store-merging.c b/gcc/gimple-ssa-store-merging.c index 1740c9ee1c1..35df0fee955 100644 --- a/gcc/gimple-ssa-store-merging.c +++ b/gcc/gimple-ssa-store-merging.c @@ -434,14 +434,14 @@ find_bswap_or_nop_load (gimple *stmt, tree ref, struct symbolic_number *n) return true; } -/* Compute the symbolic number N representing the result of a bitwise OR on 2 - symbolic number N1 and N2 whose source statements are respectively - SOURCE_STMT1 and SOURCE_STMT2. */ +/* Compute the symbolic number N representing the result of a bitwise OR, + bitwise XOR or plus on 2 symbolic number N1 and N2 whose source statements + are respectively SOURCE_STMT1 and SOURCE_STMT2. CODE is the operation. */ gimple * perform_symbolic_merge (gimple *source_stmt1, struct symbolic_number *n1, gimple *source_stmt2, struct symbolic_number *n2, - struct symbolic_number *n) + struct symbolic_number *n, enum tree_code code) { int i, size; uint64_t mask; @@ -563,7 +563,9 @@ perform_symbolic_merge (gimple *source_stmt1, struct symbolic_number *n1, masked1 = n1->n & mask; masked2 = n2->n & mask; - if (masked1 && masked2 && masked1 != masked2) + /* For BIT_XOR_EXPR or PLUS_EXPR, at least one of masked1 and masked2 + has to be 0, for BIT_IOR_EXPR x | x is still x. */ + if (masked1 && masked2 && (code != BIT_IOR_EXPR || masked1 != masked2)) return NULL; } n->n = n1->n | n2->n; @@ -769,7 +771,8 @@ find_bswap_or_nop_1 (gimple *stmt, struct symbolic_number *n, int limit) return NULL; source_stmt - = perform_symbolic_merge (source_stmt1, &n1, source_stmt2, &n2, n); + = perform_symbolic_merge (source_stmt1, &n1, source_stmt2, &n2, n, + code); if (!source_stmt) return NULL; @@ -943,7 +946,8 @@ find_bswap_or_nop (gimple *stmt, struct symbolic_number *n, bool *bswap, else if (!do_shift_rotate (LSHIFT_EXPR, &n0, eltsz)) return NULL; ins_stmt - = perform_symbolic_merge (ins_stmt, &n0, source_stmt, &n1, n); + = perform_symbolic_merge (ins_stmt, &n0, source_stmt, &n1, n, + BIT_IOR_EXPR); if (!ins_stmt) return NULL; @@ -2881,7 +2885,7 @@ imm_store_chain_info::try_coalesce_bswap (merged_store_group *merged_store, end = MAX (end, info->bitpos + info->bitsize); ins_stmt = perform_symbolic_merge (ins_stmt, &n, info->ins_stmt, - &this_n, &n); + &this_n, &n, BIT_IOR_EXPR); if (ins_stmt == NULL) return false; } diff --git a/gcc/testsuite/gcc.c-torture/execute/pr103376.c b/gcc/testsuite/gcc.c-torture/execute/pr103376.c new file mode 100644 index 00000000000..22e2019105a --- /dev/null +++ b/gcc/testsuite/gcc.c-torture/execute/pr103376.c @@ -0,0 +1,29 @@ +/* PR tree-optimization/103376 */ + +long long a = 0x123456789abcdef0LL, f; +int b, c, *d; + +__attribute__((noipa)) void +foo (int x) +{ + asm volatile ("" : : "r" (x)); +} + +int +main () +{ + long long e; + e = a; + if (b) + { + foo (c); + d = (int *) 0; + while (*d) + ; + } + f = a ^ e; + asm volatile ("" : "+m" (f)); + if (f != 0) + __builtin_abort (); + return 0; +}