[PATCH] RISC-V: Fix the warning of temporary object dangling references.

[Dongyan Chen]

During the GCC compilation, some warnings about temporary object dangling 
references emerged. They appeared in these code lines in riscv-common.cc:
const riscv_ext_info_t &implied_ext_info, const riscv_ext_info_t &ext_info = 
get_riscv_ext_info (ext) and auto &ext_info = get_riscv_ext_info (search_ext).
The issue arose because the local variable types were not used in a 
standardized way, causing their references to dangle once the function ended.
To fix this, the patch converts the const char* type to std::string via forced 
type conversion, thereby eliminating the warnings.

gcc/ChangeLog:

        * common/config/riscv/riscv-common.cc 
(riscv_ext_info_t::apply_implied_ext): Type conversion.
        (riscv_subset_list::handle_implied_ext): Ditto.
        (riscv_minimal_hwprobe_feature_bits): Ditto.

---
 gcc/common/config/riscv/riscv-common.cc | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/gcc/common/config/riscv/riscv-common.cc 
b/gcc/common/config/riscv/riscv-common.cc
index 53ca03910b38..c2e35dfe54d2 100644
--- a/gcc/common/config/riscv/riscv-common.cc
+++ b/gcc/common/config/riscv/riscv-common.cc
@@ -245,8 +245,9 @@ riscv_ext_info_t::apply_implied_ext (riscv_subset_list 
*subset_list) const
       subset_list->add (implied_info.implied_ext, true);

       /* Recursively add implied extension by implied_info->implied_ext.  */
+      std::string implied_ext_str = implied_info.implied_ext;
       const riscv_ext_info_t &implied_ext_info
-       = get_riscv_ext_info (implied_info.implied_ext);
+       = get_riscv_ext_info (implied_ext_str);
       implied_ext_info.apply_implied_ext (subset_list);
     }
   return any_change;
@@ -1089,7 +1090,8 @@ riscv_subset_list::parse_single_std_ext (const char *p, 
bool exact_single_p)
 void
 riscv_subset_list::handle_implied_ext (const char *ext)
 {
-  const riscv_ext_info_t &ext_info = get_riscv_ext_info (ext);
+  std::string ext_str = ext;
+  const riscv_ext_info_t &ext_info = get_riscv_ext_info (ext_str);
   ext_info.apply_implied_ext (this);

   /* For RISC-V ISA version 2.2 or earlier version, zicsr and zifence is
@@ -1642,7 +1644,8 @@ riscv_minimal_hwprobe_feature_bits (const char *isa,
          search_q.pop ();

          /* Iterate through the implied extension table.  */
-         auto &ext_info = get_riscv_ext_info (search_ext);
+         std::string search_ext_str = search_ext;
+         auto &ext_info = get_riscv_ext_info (search_ext_str);
          for (const auto &implied_ext : ext_info.implied_exts ())
            {
              /* When the search extension matches the implied extension and
--
2.43.0