This option (enabled by default) controls optimizations which convert
a sequence of operations into an equivalent sequence that includes
calls to builtin functions. Typical cases here are code which matches
memcpy, calloc, sincos.
The -ftree-loop-distribute-patterns flag only covers converting loops
into builtin calls, not numerous other places where knowledge of
builtin function semantics changes the generated code.
The goal is to allow built-in functions to be declared by the compiler
and used directly by the application, but to disable optimizations
which create new calls to them, and to allow this optimization
behavior to be changed for individual functions by decorating the
function definition like this:
void
attribute((optimize("no-opt-builtin")))
sincos(double x, double *s, double *c)
{
*s = sin(x);
*c = cos(x);
}
This also avoids converting loops into library calls like this:
void *
attribute((optimize("no-opt-builtin")))
memcpy(void *__restrict__ dst, const void *__restrict__ src, size_t n)
{
char *d = dst;
const char *s = src;
while (n--)
*d++ = *s++;
return dst;
}
As well as disabling analysis of memory lifetimes around free as in
this example:
void *
attribute((optimize("no-opt-builtin")))
erase_and_free(void *ptr)
{
memset(ptr, '\0', malloc_usable_size(ptr));
free(ptr);
}
Clang has a more sophisticated version of this mechanism which
can disable all builtins, or disable a specific builtin:
double
attribute((no_builtin("exp2")))
exp2(double x)
{
return pow (2.0, x);
}
Signed-off-by: Keith Packard <kei...@keithp.com>
---
gcc/builtins.c | 6 ++++++
gcc/common.opt | 4 ++++
gcc/gimple.c | 3 +++
gcc/tree-loop-distribution.c | 2 ++
4 files changed, 15 insertions(+)
diff --git a/gcc/builtins.c b/gcc/builtins.c
index 7d0f61fc98b..7aae57deab5 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -1922,6 +1922,9 @@ mathfn_built_in_2 (tree type, combined_fn fn)
built_in_function fcodef64x = END_BUILTINS;
built_in_function fcodef128x = END_BUILTINS;
+ if (flag_no_opt_builtin)
+ return END_BUILTINS;
+
switch (fn)
{
#define SEQ_OF_CASE_MATHFN \
@@ -2125,6 +2128,9 @@ mathfn_built_in_type (combined_fn fn)
case CFN_BUILT_IN_##MATHFN##L_R: \
return long_double_type_node;
+ if (flag_no_opt_builtin)
+ return NULL_TREE;
+
switch (fn)
{
SEQ_OF_CASE_MATHFN
diff --git a/gcc/common.opt b/gcc/common.opt
index eeba1a727f2..d6111cc776a 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2142,6 +2142,10 @@ fomit-frame-pointer
Common Var(flag_omit_frame_pointer) Optimization
When possible do not generate stack frames.
+fopt-builtin
+Common Var(flag_no_opt_builtin, 0) Optimization
+Match code sequences equivalent to builtin functions
+
fopt-info
Common Var(flag_opt_info) Optimization
Enable all optimization info dumps on stderr.
diff --git a/gcc/gimple.c b/gcc/gimple.c
index 22dd6417d19..5b82b9409c0 100644
--- a/gcc/gimple.c
+++ b/gcc/gimple.c
@@ -2790,6 +2790,9 @@ gimple_builtin_call_types_compatible_p (const gimple
*stmt, tree fndecl)
{
gcc_checking_assert (DECL_BUILT_IN_CLASS (fndecl) != NOT_BUILT_IN);
+ if (flag_no_opt_builtin)
+ return false;
+
tree ret = gimple_call_lhs (stmt);
if (ret
&& !useless_type_conversion_p (TREE_TYPE (ret),
diff --git a/gcc/tree-loop-distribution.c b/gcc/tree-loop-distribution.c
index 583c01a42d8..43f22a3c7ce 100644
--- a/gcc/tree-loop-distribution.c
+++ b/gcc/tree-loop-distribution.c
@@ -1859,6 +1859,7 @@ loop_distribution::classify_partition (loop_p loop,
/* Perform general partition disqualification for builtins. */
if (volatiles_p
+ || flag_no_opt_builtin
|| !flag_tree_loop_distribute_patterns)
return has_reduction;
@@ -3764,6 +3765,7 @@ loop_distribution::execute (function *fun)
/* Don't distribute multiple exit edges loop, or cold loop when
not doing pattern detection. */
if (!single_exit (loop)
+ || flag_no_opt_builtin
|| (!flag_tree_loop_distribute_patterns
&& !optimize_loop_for_speed_p (loop)))
continue;
--
2.33.0
