Hi all!
Here's a simple optimization patch for Asan. It stores alignment
information into ASAN_CHECK which is then extracted by sanopt to reduce
number of "and 0x7" instructions for sufficiently aligned accesses. I
checked it on linux kernel by comparing results of objdump -d -j .text
vmlinux | grep "and.*0x7," for optimized and regular cases. It
eliminates 12% of and 0x7's.
No regressions. Sanitized GCC was successfully Asan-bootstrapped. No
false positives were found in kernel.
--Marat
gcc/ChangeLog:
2014-09-02 Marat Zakirov <m.zaki...@samsung.com>
* asan.c (build_check_stmt): Alignment arg was added.
(asan_expand_check_ifn): Optimization for alignment >= 8.
gcc/testsuite/ChangeLog:
2014-09-02 Marat Zakirov <m.zaki...@samsung.com>
* c-c++-common/asan/red-align-1.c: New test.
* c-c++-common/asan/red-align-2.c: New test.
diff --git a/gcc/asan.c b/gcc/asan.c
index 58e7719..aed5ede 100644
--- a/gcc/asan.c
+++ b/gcc/asan.c
@@ -1639,9 +1639,11 @@ build_check_stmt (location_t loc, tree base, tree len,
if (end_instrumented)
flags |= ASAN_CHECK_END_INSTRUMENTED;
- g = gimple_build_call_internal (IFN_ASAN_CHECK, 3,
+ g = gimple_build_call_internal (IFN_ASAN_CHECK, 4,
build_int_cst (integer_type_node, flags),
- base, len);
+ base, len,
+ build_int_cst (integer_type_node,
+ align/BITS_PER_UNIT));
gimple_set_location (g, loc);
if (before_p)
gsi_insert_before (&gsi, g, GSI_SAME_STMT);
@@ -2434,6 +2436,7 @@ asan_expand_check_ifn (gimple_stmt_iterator *iter, bool use_calls)
tree base = gimple_call_arg (g, 1);
tree len = gimple_call_arg (g, 2);
+ HOST_WIDE_INT align = tree_to_shwi (gimple_call_arg (g, 3));
HOST_WIDE_INT size_in_bytes
= is_scalar_access && tree_fits_shwi_p (len) ? tree_to_shwi (len) : -1;
@@ -2547,7 +2550,10 @@ asan_expand_check_ifn (gimple_stmt_iterator *iter, bool use_calls)
gimple shadow_test = build_assign (NE_EXPR, shadow, 0);
gimple_seq seq = NULL;
gimple_seq_add_stmt (&seq, shadow_test);
- gimple_seq_add_stmt (&seq, build_assign (BIT_AND_EXPR, base_addr, 7));
+ /* Aligned (>= 8 bytes) access do not need & 7. */
+ if (align < 8)
+ gimple_seq_add_stmt (&seq, build_assign (BIT_AND_EXPR,
+ base_addr, 7));
gimple_seq_add_stmt (&seq, build_type_cast (shadow_type,
gimple_seq_last (seq)));
if (real_size_in_bytes > 1)
diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
index 7ae60f3..54ade9f 100644
--- a/gcc/internal-fn.def
+++ b/gcc/internal-fn.def
@@ -55,4 +55,4 @@ DEF_INTERNAL_FN (UBSAN_CHECK_SUB, ECF_CONST | ECF_LEAF | ECF_NOTHROW, NULL)
DEF_INTERNAL_FN (UBSAN_CHECK_MUL, ECF_CONST | ECF_LEAF | ECF_NOTHROW, NULL)
DEF_INTERNAL_FN (ABNORMAL_DISPATCHER, ECF_NORETURN, NULL)
DEF_INTERNAL_FN (BUILTIN_EXPECT, ECF_CONST | ECF_LEAF | ECF_NOTHROW, NULL)
-DEF_INTERNAL_FN (ASAN_CHECK, ECF_TM_PURE | ECF_LEAF | ECF_NOTHROW, ".W..")
+DEF_INTERNAL_FN (ASAN_CHECK, ECF_TM_PURE | ECF_LEAF | ECF_NOTHROW, ".W...")
diff --git a/gcc/testsuite/c-c++-common/asan/red-align-1.c b/gcc/testsuite/c-c++-common/asan/red-align-1.c
new file mode 100644
index 0000000..1edb3a2
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/asan/red-align-1.c
@@ -0,0 +1,20 @@
+/* This tests aligment propagation to structure elem and
+ abcense of redudant & 7. */
+
+/* { dg-options "-fdump-tree-sanopt" } */
+/* { dg-do compile } */
+/* { dg-skip-if "" { *-*-* } { "-flto" } { "" } } */
+
+struct st {
+ int a;
+ int b;
+ int c;
+} __attribute__((aligned(16)));
+
+int foo (struct st * s_p)
+{
+ return s_p->a;
+}
+
+/* { dg-final { scan-tree-dump-times "& 7" 0 "sanopt" } } */
+/* { dg-final { cleanup-tree-dump "sanopt" } } */
diff --git a/gcc/testsuite/c-c++-common/asan/red-align-2.c b/gcc/testsuite/c-c++-common/asan/red-align-2.c
new file mode 100644
index 0000000..161fe3c
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/asan/red-align-2.c
@@ -0,0 +1,20 @@
+/* This tests aligment propagation to structure elem and
+ abcense of redudant & 7. */
+
+/* { dg-options "-fdump-tree-sanopt" } */
+/* { dg-do compile } */
+/* { dg-skip-if "" { *-*-* } { "-flto" } { "" } } */
+
+struct st {
+ int a;
+ int b;
+ int c;
+} __attribute__((aligned(16)));
+
+int foo (struct st * s_p)
+{
+ return s_p->b;
+}
+
+/* { dg-final { scan-tree-dump-times "& 7" 1 "sanopt" } } */
+/* { dg-final { cleanup-tree-dump "sanopt" } } */
