[gcc r17-3263] Re: [PATCH] RISC-V: Don't emit a separate multilib for the default march/mabi

https://gcc.gnu.org/g:6294f1d9e7536e5ffcde09d1528c918d63abfef5

commit r17-3263-g6294f1d9e7536e5ffcde09d1528c918d63abfef5
Author: Jim Lin <[email protected]>
Date:   Thu Aug 13 11:46:58 2026 -0600

    Re: [PATCH] RISC-V: Don't emit a separate multilib for the default march/mabi
    
    Skip a multilib only when it is exactly equivalent to the default: it
    shares the default march and mabi and carries no other distinguishing
    option (such as mcmodel).  A multilib that matches the default march/mabi
    but differs in another option is kept.
    
    This fixes a broken Ada build.  When configured with
    --with-multilib-list=lp64d, the lp64d multilib is the default but was
    still emitted as a separate multilib, so MULTISUBDIR became /lib64/lp64d
    instead of empty.
    
    gcc/ChangeLog:
    
            * common/config/riscv/riscv-common.cc
            (riscv_multi_lib_info_t::parse): Skip a multilib that is exactly
            equivalent to the default march/mabi.
    
    Signed-off-by: Jim Lin <[email protected]>

Diff:
---
 gcc/common/config/riscv/riscv-common.cc | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/gcc/common/config/riscv/riscv-common.cc b/gcc/common/config/riscv/riscv-common.cc
index 6bbbacab8df4..83e22e0e2989 100644
--- a/gcc/common/config/riscv/riscv-common.cc
+++ b/gcc/common/config/riscv/riscv-common.cc
@@ -1922,11 +1922,21 @@ riscv_multi_lib_info_t::parse (
   else
     {
       std::vector<std::string>::const_iterator itr;
+      bool only_arch_abi = true;
       for (itr = conds.begin (); itr != conds.end (); ++itr)
 	if (prefixed_with (*itr, "march="))
 	  multi_lib_info->arch_str = itr->c_str () + strlen ("march=");
 	else if (prefixed_with (*itr, "mabi="))
 	  multi_lib_info->abi_str = itr->c_str () + strlen ("mabi=");
+	else
+	  only_arch_abi = false;
+
+      /* Skip a multi-lib that is exactly equivalent to the default: same
+	 march and mabi with no other distinguishing option. */
+      if (only_arch_abi
+	  && multi_lib_info->arch_str == default_arch_str
+	  && multi_lib_info->abi_str == default_abi_str)
+	return false;
     }
 
   multi_lib_info->subset_list =