[to-be-committed] [RISC-V] Use pack to handle repeating constants

This patch utilizes zbkb to improve the code we generate for 64bit constants
when the high half is a duplicate of the low half.

Basically we generate the low half and use a pack instruction with that same
register repeated.  ie

pack dest,src,src

That gives us a maximum sequence of 3 instructions and sometimes it will be
just 2 instructions (say if the low 32bits can be constructed with a single
addi or lui).

As with shadd, I'm abusing an RTL opcode.  This time it's CONCAT.  It's
reasonably close to what we're doing.  Obviously it's just how we identify the
desire to generate a pack in the array of opcodes.  We don't actually emit a
CONCAT.

Note that we don't care about the potential sign extension from bit 31. pack
will only look at bits 0..31 of each input (for rv64).  So we go ahead and sign
extend before synthesizing the low part as that allows us to handle more cases
trivially.

I had my testsuite generator chew on random cases of a repeating constant
without any surprises.  I don't see much point in including all those in the
testcase (after all there's 2**32 of them).  I've got a set of 10 I'm
including.  Nothing particularly interesting in them.

An enterprising developer that needs this improved without zbkb could probably
do so with a bit of work.  First increase the cost by 1 unit. Second avoid
cases where bit 31 is set and restrict it to cases when we can still create
pseudos.   On the codegen side, when encountering the CONCAT, generate the
appropriate shift of "X" into a temporary register, then IOR the temporary with
"X" into the new destination.

Anyway, I've tested this in my tester (though it doesn't turn on zbkb, yet).
I'll let the CI system chew on it overnight, but like mine, I don't think it
lights up zbkb.  So it's unlikely to spit out anything interesting.

gcc/
	* config/riscv/crypto.md (riscv_xpack_<X:mode>_<HX:mode>_2): Remove '*'
	allow it to be used via the gen_* interface.
	* config/riscv/riscv.cc (riscv_build_integer): Identify when Zbkb
	can be used to profitably synthesize repeating constants.
	(riscv_move_integer): Codegen changes to generate those Zbkb sequences.

gcc/testsuite/

	* gcc.target/riscv/synthesis-9.c: New test.

diff --git a/gcc/config/riscv/crypto.md b/gcc/config/riscv/crypto.md
index b632312ade294686df86ca2a0404348d15fd24cb..b9cac78fce1cb9a23b692feffa2c0fa0b8e1ae9f 100644 (file)
--- a/gcc/config/riscv/crypto.md
+++ b/gcc/config/riscv/crypto.md
@@ -107,7 +107,7 @@
 ;; This is slightly more complex than the other pack patterns
 ;; that fully expose the RTL as it needs to self-adjust to
 ;; rv32 and rv64.  But it's not that hard.
-(define_insn "*riscv_xpack_<X:mode>_2"
+(define_insn "riscv_xpack_<X:mode>_<HX:mode>_2"
   [(set (match_operand:X 0 "register_operand" "=r")
        (ior:X (ashift:X (match_operand:X 1 "register_operand" "r")
                         (match_operand 2 "immediate_operand" "n"))

diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index a99211d56b145c2207f05d0d762d283bb56aa371..91fefacee80c672ac6116b1a5db7ee0717b306c2 100644 (file)
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -1123,6 +1123,22 @@ riscv_build_integer (struct riscv_integer_op *codes, HOST_WIDE_INT value,
        }
     }
 
+  /* With pack we can generate a 64 bit constant with the same high
+     and low 32 bits triviall.  */
+  if (cost > 3 && TARGET_64BIT && TARGET_ZBKB)
+    {
+      unsigned HOST_WIDE_INT loval = value & 0xffffffff;
+      unsigned HOST_WIDE_INT hival = value & ~loval;
+      if (hival >> 32 == loval)
+       {
+         cost = 1 + riscv_build_integer_1 (codes, sext_hwi (loval, 32), mode);
+         codes[cost - 1].code = CONCAT;
+         codes[cost - 1].value = 0;
+         codes[cost - 1].use_uw = false;
+       }
+
+    }
+
   return cost;
 }
 
@@ -2679,6 +2695,13 @@ riscv_move_integer (rtx temp, rtx dest, HOST_WIDE_INT value,
              rtx t = can_create_pseudo_p () ? gen_reg_rtx (mode) : temp;
              x = riscv_emit_set (t, x);
            }
+         else if (codes[i].code == CONCAT)
+           {
+             rtx t = can_create_pseudo_p () ? gen_reg_rtx (mode) : temp;
+             rtx t2 = gen_lowpart (SImode, x);
+             emit_insn (gen_riscv_xpack_di_si_2 (t, x, GEN_INT (32), t2));
+             x = t;
+           }
          else
            x = gen_rtx_fmt_ee (codes[i].code, mode,
                                x, GEN_INT (codes[i].value));

diff --git a/gcc/testsuite/gcc.target/riscv/synthesis-9.c b/gcc/testsuite/gcc.target/riscv/synthesis-9.c
new file mode 100644 (file)
index 0000000..cc62218
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/synthesis-9.c
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target rv64 } */
+/* We aggressively skip as we really just need to test the basic synthesis
+   which shouldn't vary based on the optimization level.  -O1 seems to work
+   and eliminates the usual sources of extraneous dead code that would throw
+   off the counts.  */
+/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" "-O2" "-O3" "-Os" "-Oz" "-flto" } } */
+/* { dg-options "-march=rv64gc_zba_zbb_zbkb_zbs" } */
+
+/* Rather than test for a specific synthesis of all these constants or
+   having thousands of tests each testing one variant, we just test the
+   total number of instructions.
+
+   This isn't expected to change much and any change is worthy of a look.  */
+/* { dg-final { scan-assembler-times "\\t(add|addi|bseti|li|pack|ret|sh1add|sh2add|sh3add|slli|srli|xori)" 40 } } */
+
+
+
+unsigned long foo_0xf857f2def857f2de(void) { return 0xf857f2def857f2deUL; }
+unsigned long foo_0x99660e6399660e63(void) { return 0x99660e6399660e63UL; }
+unsigned long foo_0x937f1b75937f1b75(void) { return 0x937f1b75937f1b75UL; }
+unsigned long foo_0xb5019fa0b5019fa0(void) { return 0xb5019fa0b5019fa0UL; }
+unsigned long foo_0xb828e6c1b828e6c1(void) { return 0xb828e6c1b828e6c1UL; }
+unsigned long foo_0x839d87e9839d87e9(void) { return 0x839d87e9839d87e9UL; }
+unsigned long foo_0xc29617c1c29617c1(void) { return 0xc29617c1c29617c1UL; }
+unsigned long foo_0xa4118119a4118119(void) { return 0xa4118119a4118119UL; }
+unsigned long foo_0x8c01df7d8c01df7d(void) { return 0x8c01df7d8c01df7dUL; }
+unsigned long foo_0xf0e23d6bf0e23d6b(void) { return 0xf0e23d6bf0e23d6bUL; }