[gcc(refs/vendors/riscv/heads/gcc-14-with-riscv-opts)] [RISC-V] Avoid unnecessary sign extension after memcmp

[Jeff Law via Gcc-cvs]

https://gcc.gnu.org/g:67116d59607d1897629deb3b95f7ccb9d4d875cb

commit 67116d59607d1897629deb3b95f7ccb9d4d875cb
Author: Jeff Law <j...@ventanamicro.com>
Date:   Fri Jul 12 07:53:41 2024 -0600

    [RISC-V] Avoid unnecessary sign extension after memcmp
    
    Similar to the str[n]cmp work, this adjusts the block compare expansion to 
do
    its work in X mode with an appropriate lowpart extraction of the results at 
the
    end of the sequence.
    
    This has gone through my tester on rv32 and rv64, but that's it. Waiting on
    pre-commit testing before moving forward.
    
    gcc/
    
            * config/riscv/riscv-string.cc 
(emit_memcmp_scalar_load_and_compare):
            Set RESULT directly rather than using a temporary.
            (emit_memcmp_scalar_result_calculation): Similarly.
            (riscv_expand_block_compare_scalar): Use CONST0_RTX rather than
            generating new RTL.
            * config/riscv/riscv.md (cmpmemsi): Pass an X mode temporary to the
            expansion routines.  If necessary extract low part of the word to 
store
            in final result location.
    
    (cherry picked from commit ae829a27785307232e4db0df6a30ca275941b613)

Diff:
---
 gcc/config/riscv/riscv-string.cc | 15 ++++++---------
 gcc/config/riscv/riscv.md        | 14 ++++++++++++--
 2 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/gcc/config/riscv/riscv-string.cc b/gcc/config/riscv/riscv-string.cc
index 4736228e6f14..80d22e87d571 100644
--- a/gcc/config/riscv/riscv-string.cc
+++ b/gcc/config/riscv/riscv-string.cc
@@ -663,9 +663,7 @@ emit_memcmp_scalar_load_and_compare (rtx result, rtx src1, 
rtx src2,
       /* Fast-path for a single byte.  */
       if (cmp_bytes == 1)
        {
-         rtx tmp = gen_reg_rtx (Xmode);
-         do_sub3 (tmp, data1, data2);
-         emit_insn (gen_movsi (result, gen_lowpart (SImode, tmp)));
+         do_sub3 (result, data1, data2);
          emit_jump_insn (gen_jump (final_label));
          emit_barrier (); /* No fall-through.  */
          return;
@@ -702,12 +700,11 @@ emit_memcmp_scalar_result_calculation (rtx result, rtx 
data1, rtx data2)
   /* Get bytes in big-endian order and compare as words.  */
   do_bswap2 (data1, data1);
   do_bswap2 (data2, data2);
+
   /* Synthesize (data1 >= data2) ? 1 : -1 in a branchless sequence.  */
-  rtx tmp = gen_reg_rtx (Xmode);
-  emit_insn (gen_slt_3 (LTU, Xmode, Xmode, tmp, data1, data2));
-  do_neg2 (tmp, tmp);
-  do_ior3 (tmp, tmp, const1_rtx);
-  emit_insn (gen_movsi (result, gen_lowpart (SImode, tmp)));
+  emit_insn (gen_slt_3 (LTU, Xmode, Xmode, result, data1, data2));
+  do_neg2 (result, result);
+  do_ior3 (result, result, const1_rtx);
 }
 
 /* Expand memcmp using scalar instructions (incl. Zbb).
@@ -773,7 +770,7 @@ riscv_expand_block_compare_scalar (rtx result, rtx src1, 
rtx src2, rtx nbytes)
                                       data1, data2,
                                       diff_label, final_label);
 
-  emit_insn (gen_rtx_SET (result, gen_rtx_CONST_INT (SImode, 0)));
+  emit_move_insn (result, CONST0_RTX (GET_MODE (result)));
   emit_jump_insn (gen_jump (final_label));
   emit_barrier (); /* No fall-through.  */
 
diff --git a/gcc/config/riscv/riscv.md b/gcc/config/riscv/riscv.md
index 2e2379dfca4f..5dee837a5878 100644
--- a/gcc/config/riscv/riscv.md
+++ b/gcc/config/riscv/riscv.md
@@ -2675,9 +2675,19 @@
                                       operands[2], operands[3]))
     DONE;
 
-  if (riscv_expand_block_compare (operands[0], operands[1], operands[2],
+  rtx temp = gen_reg_rtx (word_mode);
+  if (riscv_expand_block_compare (temp, operands[1], operands[2],
                                   operands[3]))
-    DONE;
+    {
+      if (TARGET_64BIT)
+       {
+         temp = gen_lowpart (SImode, temp);
+         SUBREG_PROMOTED_VAR_P (temp) = 1;
+         SUBREG_PROMOTED_SET (temp, SRP_SIGNED);
+       }
+      emit_move_insn (operands[0], temp);
+      DONE;
+    }
   else
     FAIL;
 })