[gcc(refs/vendors/vrull/heads/for-upstream)] RISC-V: Optimise adding a (larger than simm12) constant to a register

[Philipp Tomsich <ptomsich@gcc.gnu.org>]

https://gcc.gnu.org/g:c5d23bb9549f6f021a56fd4b15cbaa7063c5ac49

commit c5d23bb9549f6f021a56fd4b15cbaa7063c5ac49
Author: Philipp Tomsich <philipp.tomsich@vrull.eu>
Date:   Wed Oct 12 14:45:42 2022 +0200

    RISC-V: Optimise adding a (larger than simm12) constant to a register
    
    Handling the register-const_int addition has very quickly escalated to
    creating a full sign-extended 32bit constant and performing a
    register-register for RISC-V in GCC so far, resulting in sequences like
    (for the case of "a + 2048"):
            li      a5,4096
            addi    a5,a5,-2048
            add     a0,a0,a5
    
    By adding an expansion for add<mode>3, we can emit optimised RTL that
    matches the capabilities of RISC-V better by adding support for the
    following, previously unoptimised cases:
      - addi + addi
            addi    a0,a0,2047
            addi    a0,a0,1
      - li + sh[123]add (if Zba is enabled)
            li      a5,960
            sh3add  a0,a5,a0
    
    With this commit, we also fix up riscv_adjust_libcall_cfi_prologue()
    and riscv_adjust_libcall_cfi_epilogue() to not use gen_add3_insn, as
    the expander will otherwise wrap the resulting set-expression in an
    insn (causing an ICE at dwarf2-time) when invoked with -msave-restore.
    
    This closes the gap to LLVM, which has already been emitting these
    optimised sequences.
    
    Note that this benefits is perlbench (in SPEC CPU 2017), which needs
    to add the constant 3840.
    
    gcc/ChangeLog:
    
            * config/riscv/bitmanip.md (*shNadd): Rename.
            (riscv_shNadd<X:mode>): Expose as gen_riscv_shNadd{di/si}.
            * config/riscv/predicates.md (const_arith_shifted123_operand):
            New predicate (for constants that are a simm12, shifted by
            1, 2 or 3).
            (const_arith_2simm12_operand): New predicate (that can be
            expressed by adding 2 simm12 together).
            (addi_operand): New predicate (an immedaite operand suitable
            for the new add<mode>3 expansion).
            * config/riscv/riscv.cc (riscv_adjust_libcall_cfi_prologue):
            Don't use gen_add3_insn, where a RTX instead of an INSN is
            required (otherwise this will break as soon as we have a
            define_expand for add<mode>3).
            (riscv_adjust_libcall_cfi_epilogue): Same.
            * config/riscv/riscv.md (addsi3): Rename.
            (riscv_addsi3): New name for addsi3.
            (adddi3): Rename.
            (riscv_adddi3): New name for adddi3.
            (add<mode>3): New expander that handles the basic and fancy
            (such as li+sh[123]add, addi+addi, ...) cases for adding
            register-register and register-const_int.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.target/riscv/addi.c: New test.
            * gcc.target/riscv/zba-shNadd-06.c: New test.
    
    Series-to: gcc-patches@gcc.gnu.org
    Series-cc: Palmer Dabbelt <palmer@rivosinc.com>
    Series-cc: Vineet Gupta <vineetg@rivosinc.com>
    Series-cc: Christoph Muellner <christoph.muellner@vrull.eu>
    Series-cc: Kito Cheng <kito.cheng@gmail.com>
    Series-cc: Jeff Law <jlaw@ventanamicro.com>

Diff:
---
 gcc/config/riscv/bitmanip.md                   |  2 +-
 gcc/config/riscv/predicates.md                 | 28 +++++++++++++
 gcc/config/riscv/riscv.cc                      | 10 +++--
 gcc/config/riscv/riscv.md                      | 58 +++++++++++++++++++++++++-
 gcc/testsuite/gcc.target/riscv/addi.c          | 39 +++++++++++++++++
 gcc/testsuite/gcc.target/riscv/zba-shNadd-06.c | 11 +++++
 6 files changed, 141 insertions(+), 7 deletions(-)

diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md
index 8b6a7cad3f6..7e059fb5903 100644
--- a/gcc/config/riscv/bitmanip.md
+++ b/gcc/config/riscv/bitmanip.md
@@ -29,7 +29,7 @@
   [(set_attr "type" "bitmanip,load")
    (set_attr "mode" "DI")])
 
-(define_insn "*shNadd"
+(define_insn "riscv_shNadd<X:mode>"
   [(set (match_operand:X 0 "register_operand" "=r")
 	(plus:X (ashift:X (match_operand:X 1 "register_operand" "r")
 			  (match_operand:QI 2 "imm123_operand" "Ds3"))
diff --git a/gcc/config/riscv/predicates.md b/gcc/config/riscv/predicates.md
index 6772228e5b6..c56bfa99339 100644
--- a/gcc/config/riscv/predicates.md
+++ b/gcc/config/riscv/predicates.md
@@ -308,3 +308,31 @@
 		 (match_test "INTVAL (op) > 0")))
        (ior (match_test "SMALL_OPERAND (UINTVAL (op) & ~(HOST_WIDE_INT_1U << floor_log2 (UINTVAL (op))))")
 	    (match_test "popcount_hwi (UINTVAL (op)) == 2"))))
+
+;; A CONST_INT that can be shifted down by 1, 2 or 3 bits (i.e., has
+;; these bits clear) and will then form a SMALL_OPERAND.
+(define_predicate "const_arith_shifted123_operand"
+  (and (match_code "const_int")
+       (not (match_test "SMALL_OPERAND (INTVAL (op))")))
+{
+  HOST_WIDE_INT val = INTVAL (op);
+  int trailing = ctz_hwi (val);
+
+  /* Clamp to 3, as we have sh[123]add instructions only. */
+  if (trailing > 3)
+     trailing = 3;
+
+  return trailing > 0 && SMALL_OPERAND (val >> trailing);
+})
+
+;; A CONST_INT that can formed by adding two SMALL_OPERANDs together
+(define_predicate "const_arith_2simm12_operand"
+  (and (match_code "const_int")
+       (ior (match_test "SMALL_OPERAND(INTVAL (op) - ~(HOST_WIDE_INT_M1U << (IMM_BITS - 1)))")
+	    (match_test "SMALL_OPERAND(INTVAL (op) -  (HOST_WIDE_INT_M1U << (IMM_BITS - 1)))"))))
+
+(define_predicate "addi_operand"
+  (ior (match_operand 0 "arith_operand")
+       (match_operand 0 "const_arith_2simm12_operand")
+       (and (match_operand 0 "const_arith_shifted123_operand")
+	    (match_test "TARGET_ZBA"))))
diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index 737ec51b593..451ec7034c6 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -4955,8 +4955,9 @@ riscv_adjust_libcall_cfi_prologue ()
       }
 
   /* Debug info for adjust sp.  */
-  adjust_sp_rtx = gen_add3_insn (stack_pointer_rtx,
-				 stack_pointer_rtx, GEN_INT (-saved_size));
+  adjust_sp_rtx = gen_rtx_SET (stack_pointer_rtx,
+			       gen_rtx_PLUS (Pmode, stack_pointer_rtx,
+					     GEN_INT (-saved_size)));
   dwarf = alloc_reg_note (REG_CFA_ADJUST_CFA, adjust_sp_rtx,
 			  dwarf);
   return dwarf;
@@ -5077,8 +5078,9 @@ riscv_adjust_libcall_cfi_epilogue ()
   int saved_size = cfun->machine->frame.save_libcall_adjustment;
 
   /* Debug info for adjust sp.  */
-  adjust_sp_rtx = gen_add3_insn (stack_pointer_rtx,
-				 stack_pointer_rtx, GEN_INT (saved_size));
+  adjust_sp_rtx = gen_rtx_SET (stack_pointer_rtx,
+			       gen_rtx_PLUS (Pmode, stack_pointer_rtx,
+					     GEN_INT (saved_size)));
   dwarf = alloc_reg_note (REG_CFA_ADJUST_CFA, adjust_sp_rtx,
 			  dwarf);
 
diff --git a/gcc/config/riscv/riscv.md b/gcc/config/riscv/riscv.md
index 8c4961315a0..64bf30f7720 100644
--- a/gcc/config/riscv/riscv.md
+++ b/gcc/config/riscv/riscv.md
@@ -449,7 +449,7 @@
   [(set_attr "type" "fadd")
    (set_attr "mode" "<UNITMODE>")])
 
-(define_insn "addsi3"
+(define_insn "riscv_addsi3"
   [(set (match_operand:SI          0 "register_operand" "=r,r")
 	(plus:SI (match_operand:SI 1 "register_operand" " r,r")
 		 (match_operand:SI 2 "arith_operand"    " r,I")))]
@@ -458,7 +458,7 @@
   [(set_attr "type" "arith")
    (set_attr "mode" "SI")])
 
-(define_insn "adddi3"
+(define_insn "riscv_adddi3"
   [(set (match_operand:DI          0 "register_operand" "=r,r")
 	(plus:DI (match_operand:DI 1 "register_operand" " r,r")
 		 (match_operand:DI 2 "arith_operand"    " r,I")))]
@@ -467,6 +467,60 @@
   [(set_attr "type" "arith")
    (set_attr "mode" "DI")])
 
+(define_expand "add<mode>3"
+  [(set (match_operand:GPR           0 "register_operand"      "=r,r")
+	(plus:GPR (match_operand:GPR 1 "register_operand"      " r,r")
+		  (match_operand:GPR 2 "addi_operand"          " r,I")))]
+  ""
+{
+  if (arith_operand (operands[2], <MODE>mode))
+    emit_insn (gen_riscv_add<mode>3 (operands[0], operands[1], operands[2]));
+  else if (const_arith_2simm12_operand (operands[2], <MODE>mode))
+    {
+      /* Split into two immediates that add up to the desired value:
+       * e.g., break up "a + 2445" into:
+       *         addi	a0,a0,2047
+       *	 addi	a0,a0,398
+       */
+
+      HOST_WIDE_INT val = INTVAL (operands[2]);
+      HOST_WIDE_INT saturated = HOST_WIDE_INT_M1U << (IMM_BITS - 1);
+
+      if (val >= 0)
+	 saturated = ~saturated;
+
+      val -= saturated;
+
+      rtx tmp = gen_reg_rtx (<MODE>mode);
+      emit_insn (gen_riscv_add<mode>3 (tmp, operands[1], GEN_INT (saturated)));
+      emit_insn (gen_riscv_add<mode>3 (operands[0], tmp, GEN_INT (val)));
+    }
+  else if (<MODE>mode == word_mode
+	   && const_arith_shifted123_operand (operands[2], <MODE>mode))
+    {
+      /* Use a sh[123]add and an immediate shifted down by 1, 2, or 3. */
+
+      HOST_WIDE_INT val = INTVAL (operands[2]);
+      int shamt = ctz_hwi (val);
+
+      if (shamt > 3)
+	shamt = 3;
+
+      rtx tmp = gen_reg_rtx (<MODE>mode);
+      emit_insn (gen_rtx_SET (tmp, GEN_INT (val >> shamt)));
+
+      /* We don't use gen_riscv_shNadd here, as it will only exist for
+	 <X:mode>.  Instead we build up its canonical form directly.  */
+      rtx shifted_imm = gen_rtx_ASHIFT (<MODE>mode, tmp, GEN_INT (shamt));
+      rtx shNadd = gen_rtx_PLUS (<MODE>mode, shifted_imm, operands[1]);
+      emit_insn (gen_rtx_SET (operands[0], shNadd));
+    }
+  else
+    FAIL;
+
+  DONE;
+})
+
 (define_expand "addv<mode>4"
   [(set (match_operand:GPR           0 "register_operand" "=r,r")
 	(plus:GPR (match_operand:GPR 1 "register_operand" " r,r")
diff --git a/gcc/testsuite/gcc.target/riscv/addi.c b/gcc/testsuite/gcc.target/riscv/addi.c
new file mode 100644
index 00000000000..01339e44697
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/addi.c
@@ -0,0 +1,39 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc -mabi=lp64" } */
+/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" } } */
+
+long long f (long long a)
+{
+  //	addi	a0,a0,2047
+  //	addi	a0,a0,1
+
+  return a + 2048;
+}
+
+long long f2 (long long a)
+{
+  //	addi	a0,a0,2047
+  //	addi	a0,a0,398
+
+  return a + 2445;
+}
+
+long long f3 (long long a)
+{
+  //  	addi	a0,a0,-2048
+  //	addi	a0,a0,-397
+
+  return a - 2445;
+}
+
+long long f6 (long long a)
+{
+  //  	li	a5,1179648
+  //	add	a0,a0,a5
+
+  return a + (0x12 << 16);
+}
+
+/* { dg-final { scan-assembler-times "addi\t" 6 } } */
+/* { dg-final { scan-assembler-times "li\t" 1 } } */
+/* { dg-final { scan-assembler-times "add\t" 1 } } */
diff --git a/gcc/testsuite/gcc.target/riscv/zba-shNadd-06.c b/gcc/testsuite/gcc.target/riscv/zba-shNadd-06.c
new file mode 100644
index 00000000000..c55f05ed1d2
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zba-shNadd-06.c
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc_zba -mabi=lp64" } */
+/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" } } */
+
+long long f (long long a)
+{
+  return a + 7680;
+}
+
+/* { dg-final { scan-assembler-times "li\t" 1 } } */
+/* { dg-final { scan-assembler-times "sh3add\t" 1 } } */