[gcc r13-1346] nios2: Fix PIC function call slowness

[gcc r13-1346] nios2: Fix PIC function call slowness

[Joseph Myers]

https://gcc.gnu.org/g:b01c075e7e6d84da846c2ff9087433a30ebeb0d2

commit r13-1346-gb01c075e7e6d84da846c2ff9087433a30ebeb0d2
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed Jun 29 15:55:41 2022 +0000

    nios2: Fix PIC function call slowness
    
    On Nios II, PIC function calls use R_NIOS2_CALL* relocations, which
    may refer to a GOT entry that initially points to a PLT entry to
    resolve the function on first call and that is then changed by the
    dynamic linker to point directly to the function to be called so
    subsequent calls do not go through the dynamic linker.  To quote the
    ABI, "A global offset table (GOT) entry referenced using
    R_NIOS2_GOT16, R_NIOS2_GOT_LO as well as R_NIOS2_GOT_HA must be
    resolved at load time.  A GOT entry referenced only using
    R_NIOS2_CALL16, R_NIOS2_CALL_LO as well as R_NIOS2_CALL_HA can
    initially refer to a procedure linkage table (PLT) entry and then be
    resolved lazily.".
    
    However, GCC wrongly treats function addresses loaded from the GOT
    with such relocations as constant.  If the address load is pulled out
    of a loop, then every call in the loop looks up the function by name.
    This shows up as very slow execution of many glibc testcases in glibc
    2.35 and later (tests that call functions from shared libc many times
    in a loop), where tests are now built as PIE by default.  Fix this
    problem by using gen_rtx_MEM instead of gen_const_mem when loading
    addresses for PIC function calls.
    
    Tested with no regressions for cross to nios2-linux-gnu, where many
    glibc tests pass that previously timed out.
    
            * config/nios2/nios2.cc (nios2_load_pic_address): Use gen_rtx_MEM
            not gen_const_mem for UNSPEC_PIC_CALL_SYM.

Diff:
---
 gcc/config/nios2/nios2.cc | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/gcc/config/nios2/nios2.cc b/gcc/config/nios2/nios2.cc
index f193cde5a34..1a33c88f19f 100644
--- a/gcc/config/nios2/nios2.cc
+++ b/gcc/config/nios2/nios2.cc
@@ -2552,7 +2552,10 @@ nios2_load_pic_address (rtx sym, int unspec, rtx tmp)
       return nios2_large_got_address (offset, tmp);
     }
 
-  return gen_const_mem (Pmode, nios2_got_address (sym, unspec));
+  if (unspec == UNSPEC_PIC_CALL_SYM)
+    return gen_rtx_MEM (Pmode, nios2_got_address (sym, unspec));
+  else
+    return gen_const_mem (Pmode, nios2_got_address (sym, unspec));
 }
 
 /* Nonzero if the constant value X is a legitimate general operand