[PATCH v3 2/2] RISC-V: avoid LUI based const mat in alloca epilogue expansion

[Vineet Gupta]

This is testsuite clean however there's a dwarf quirk which I want to
run by the experts. The test that was tripping CI has following
fragment:

        Before patch            |       After Patch
------------------------------------------------------
   li   t0,-4096                |  addi sp,s0,-2048
   addi t0,t0,560               |  .cfi_def_cfa 2, 2048      <- #1
   add  sp,s0,t0                |  addi sp,sp,-1488
   .cfi_def_cfa 2, 3536         |  .cfi_def_cfa_offset 3536  <- #2
   addi sp,sp,1504              |  addi sp,sp,1504
   .cfi_def_cfa_offset 2032     |  .cfi_def_cfa_offset 2032  <- #3

The dwarf insn #1 and #3 seem ok, however #2 seems dubious to me.

---

This is continuing on the prev patch in function epilogue expansion.

gcc/ChangeLog:
        * config/riscv/riscv.cc (riscv_expand_epilogue): Handle offset
        being sum of two S12.

Signed-off-by: Vineet Gupta <vine...@rivosinc.com>
---
 gcc/config/riscv/riscv.cc | 33 ++++++++++++++++++++++++++-------
 1 file changed, 26 insertions(+), 7 deletions(-)

diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index 2ecbcf1d0af8..85df5b7ab498 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -8111,7 +8111,10 @@ riscv_expand_epilogue (int style)
       need_barrier_p = false;
 
       poly_int64 adjust_offset = -frame->hard_frame_pointer_offset;
+      rtx dwarf_adj = gen_int_mode (adjust_offset, Pmode);
       rtx adjust = NULL_RTX;
+      bool sum_of_two_s12 = false;
+      HOST_WIDE_INT one, two;
 
       if (!adjust_offset.is_constant ())
        {
@@ -8123,14 +8126,23 @@ riscv_expand_epilogue (int style)
        }
       else
        {
-         if (!SMALL_OPERAND (adjust_offset.to_constant ()))
+         HOST_WIDE_INT adj_off_value = adjust_offset.to_constant ();
+         if (SMALL_OPERAND (adj_off_value))
+           {
+             adjust = GEN_INT (adj_off_value);
+           }
+         else if (SUM_OF_TWO_S12_ALGN (adj_off_value))
+           {
+             riscv_split_sum_of_two_s12 (adj_off_value, &one, &two);
+             dwarf_adj = adjust = GEN_INT (one);
+             sum_of_two_s12 = true;
+           }
+         else
            {
              riscv_emit_move (RISCV_PROLOGUE_TEMP (Pmode),
-                              GEN_INT (adjust_offset.to_constant ()));
+                              GEN_INT (adj_off_value));
              adjust = RISCV_PROLOGUE_TEMP (Pmode);
            }
-         else
-           adjust = GEN_INT (adjust_offset.to_constant ());
        }
 
       insn = emit_insn (
@@ -8138,14 +8150,21 @@ riscv_expand_epilogue (int style)
                              adjust));
 
       rtx dwarf = NULL_RTX;
-      rtx cfa_adjust_value = gen_rtx_PLUS (
-                              Pmode, hard_frame_pointer_rtx,
-                              gen_int_mode (-frame->hard_frame_pointer_offset, 
Pmode));
+      rtx cfa_adjust_value = gen_rtx_PLUS (Pmode, hard_frame_pointer_rtx,
+                                          dwarf_adj);
       rtx cfa_adjust_rtx = gen_rtx_SET (stack_pointer_rtx, cfa_adjust_value);
       dwarf = alloc_reg_note (REG_CFA_ADJUST_CFA, cfa_adjust_rtx, dwarf);
+
       RTX_FRAME_RELATED_P (insn) = 1;
 
       REG_NOTES (insn) = dwarf;
+
+      if (sum_of_two_s12)
+       {
+         insn = emit_insn (gen_add3_insn (stack_pointer_rtx, stack_pointer_rtx,
+                           GEN_INT (two)));
+         RTX_FRAME_RELATED_P (insn) = 1;
+       }
     }
 
   if (use_restore_libcall || use_multi_pop)
-- 
2.34.1