The -fmerge-constants option controls whether constants are emitted into
mergeable sections - however this applies to all constants, including
strings. On targets that support anchors it may be better to use anchors
for FP constants (eg. PR121240). Add new params string-merging-threshold
and constant-merging-threshold to allow finer grained control. The default
is zero and generated code is unchanged.
OK for commit?
gcc:
* params.opt (constant-merging-threshold): Add new param.
(string-merging-threshold): Add new param.
* varasm.cc (mergeable_string_section): Compare string size with
param_string_merging_threshold before merging.
(mergeable_constant_section): Compare constant size with
param_constant_merging_threshold before merging.
* doc/invoke.texi (string-merging-threshold): Document new param.
(constant-merging-threshold): Likewise.
---
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index
bae66ba6c45f9f23f3c97cc55eb292474db502db..8a6c8473d90f2a4798c71c8aeba77a166ccebdae
100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -18066,6 +18066,14 @@ bubbles. This is the current default. Zero means the
scheduling description
might not be available/accurate or perhaps not applicable at all, such as for
modern out-of-order processors.
+@item string-merging-threshold
+Specifies the minimum size in bytes before string constants are considered for
+merging across compilation units.
+
+@item constant-merging-threshold
+Specifies the minimum size in bytes before integer/floating-point constants
+are considered for merging across compilation units.
+
@end table
The following choices of @var{name} are available on AArch64 targets:
diff --git a/gcc/params.opt b/gcc/params.opt
index
e2b3930d5a768cb4bcd8815e2d0887190f89596e..947497fa3ac0057c9a3eed86e9db260a1b8894e1
100644
--- a/gcc/params.opt
+++ b/gcc/params.opt
@@ -130,6 +130,10 @@ The smallest number of different values for which it is
best to use a jump-table
Common Joined UInteger Var(param_comdat_sharing_probability) Init(20) Param
Optimization
Probability that COMDAT function will be shared with different compilation
unit.
+-param=constant-merging-threshold=
+Common Joined UInteger Var(param_constant_merging_threshold) Init(0) Param
Optimization
+Minimum constant size before it is considered for merging across compilation
units.
+
-param=cxx-max-namespaces-for-diagnostic-help=
Common Joined UInteger Var(param_cxx_max_namespaces_for_diagnostic_help)
Init(1000) Param
Maximum number of namespaces to search for alternatives when name lookup fails.
@@ -1107,6 +1111,10 @@ Maximum size of a single store merging region in bytes.
Common Joined UInteger Var(param_store_forwarding_max_distance) Init(10)
IntegerRange(0, 1000) Param Optimization
Maximum number of instruction distance that a small store forwarded to a
larger load may stall. Value '0' disables the cost checks for the
avoid-store-forwarding pass.
+-param=string-merging-threshold=
+Common Joined UInteger Var(param_string_merging_threshold) Init(0) Param
Optimization
+Minimum string size before it is considered for merging across compilation
units.
+
-param=switch-conversion-max-branch-ratio=
Common Joined UInteger Var(param_switch_conversion_branch_ratio) Init(8)
IntegerRange(1, 65536) Param Optimization
The maximum ratio between array size and switch branches for a switch
conversion to take place.
diff --git a/gcc/varasm.cc b/gcc/varasm.cc
index
fec792ec2326f3fb631e5d8b3538f52a57347d66..2c4669f629fcf24848d8dc6e7a5fe681a0a5b66c
100644
--- a/gcc/varasm.cc
+++ b/gcc/varasm.cc
@@ -873,6 +873,7 @@ mergeable_string_section (tree decl ATTRIBUTE_UNUSED,
&& TREE_CODE (TREE_TYPE (decl)) == ARRAY_TYPE
&& align <= MAX_MERGEABLE_BITSIZE
&& (len = int_size_in_bytes (TREE_TYPE (decl))) > 0
+ && len >= param_string_merging_threshold
&& TREE_STRING_LENGTH (decl) == len)
{
scalar_int_mode mode;
@@ -927,6 +928,7 @@ mergeable_constant_section (unsigned HOST_WIDE_INT
size_bits,
newsize = HOST_WIDE_INT_1U << ceil_log2 (size_bits);
if (HAVE_GAS_SHF_MERGE && flag_merge_constants
&& newsize <= MAX_MERGEABLE_BITSIZE
+ && (newsize / BITS_PER_UNIT) >= param_constant_merging_threshold
&& align >= 8
&& align <= newsize
&& (align & (align - 1)) == 0)
