Recently I tried to set a function's target attribute conditionally
based on template parameters, eg.:
template<bool enable_sse>
[[gnu::target (enable_sse ? "sse" : "")]]
void func () { /* ... */ }
I then discovered that this is currently not possible. This small patch
resolves that.
A possible alternative solution is to do this globally, eg. in
decl_attributes. But doing so would trigger empty-string warnings from
handle_target_attribute, and I don't know how safe it is to remove that.
There likely isn't much use for this with other attributes, anyway.
2022-10-17 Jan W. Jagersma <jwjager...@gmail.com>
gcc/ChangeLog:
* config/i386/i386-options.cc
(ix86_valid_target_attribute_inner_p): Dereference args string
from ADDR_EXPR.
gcc/testsuite/ChangeLog:
* g++.target/i386/target-attr-conditional.C: New test.
---
gcc/config/i386/i386-options.cc | 9 ++++
.../g++.target/i386/target-attr-conditional.C | 53 +++++++++++++++++++
2 files changed, 62 insertions(+)
create mode 100644 gcc/testsuite/g++.target/i386/target-attr-conditional.C
diff --git a/gcc/config/i386/i386-options.cc b/gcc/config/i386/i386-options.cc
index acb2291e70f..915f3b0c1f0 100644
--- a/gcc/config/i386/i386-options.cc
+++ b/gcc/config/i386/i386-options.cc
@@ -1123,6 +1123,15 @@ ix86_valid_target_attribute_inner_p (tree fndecl, tree
args, char *p_strings[],
= fndecl == NULL ? UNKNOWN_LOCATION : DECL_SOURCE_LOCATION (fndecl);
const char *attr_name = target_clone_attr ? "target_clone" : "target";
+ args = tree_strip_nop_conversions (args);
+
+ if (TREE_CODE (args) == ADDR_EXPR)
+ {
+ /* Attribute string is given by a constexpr function or conditional
+ expression. Dereference ADDR_EXPR, operand should be a STRING_CST. */
+ args = TREE_OPERAND (args, 0);
+ }
+
/* If this is a list, recurse to get the options. */
if (TREE_CODE (args) == TREE_LIST)
{
diff --git a/gcc/testsuite/g++.target/i386/target-attr-conditional.C
b/gcc/testsuite/g++.target/i386/target-attr-conditional.C
new file mode 100644
index 00000000000..2d418ed90bf
--- /dev/null
+++ b/gcc/testsuite/g++.target/i386/target-attr-conditional.C
@@ -0,0 +1,53 @@
+/* { dg-do compile } */
+/* { dg-options "-Wno-psabi -m32 -march=i386 -std=c++20" } */
+
+#pragma GCC push_options
+#pragma GCC target("sse")
+
+typedef int __m64 __attribute__ ((__vector_size__ (8), __may_alias__));
+typedef short __v4hi __attribute__ ((__vector_size__ (8)));
+
+extern __inline int __attribute__((__gnu_inline__, __always_inline__,
__artificial__))
+_mm_extract_pi16 (__m64 const __A, int const __N)
+{
+ return (unsigned short) __builtin_ia32_vec_ext_v4hi ((__v4hi)__A, __N);
+}
+
+#pragma GCC pop_options
+
+consteval const char*
+target_string (bool enable_sse)
+{
+ return enable_sse ? "sse" : "";
+}
+
+// Via consteval function
+template<bool enable_sse>
+[[gnu::target (target_string (enable_sse))]]
+int
+extract1 (__m64 const src)
+{
+ if constexpr (enable_sse)
+ return _mm_extract_pi16 (src, 0);
+ else
+ return reinterpret_cast<__v4hi>(src)[1];
+}
+
+// Via ternary operator
+template<bool enable_sse>
+[[gnu::target (enable_sse ? "sse" : "")]]
+int
+extract2 (__m64 const src)
+{
+ if constexpr (enable_sse)
+ return _mm_extract_pi16 (src, 2);
+ else
+ return reinterpret_cast<__v4hi>(src)[3];
+}
+
+int
+test (__m64 const src)
+{
+ return extract1<true>(src) + extract1<false>(src)
+ + extract2<true>(src) + extract2<false>(src);
+}
--
2.35.1
