Re: [PATCH] AArch64: Improve immediate generation

[Richard Earnshaw]

On 19/10/2023 13:43, Wilco Dijkstra wrote:
Further improve immediate generation by adding support for 2-instruction
MOV/EOR bitmask immediates.  This reduces the number of 3/4-instruction
immediates in SPECCPU2017 by ~2%.

Passes regress, OK for commit?

gcc/ChangeLog:
        * config/aarch64/aarch64.cc (aarch64_internal_mov_immediate)
        Add support for immediates using MOV/EOR bitmask.

gcc/testsuite:
        * gcc.target/aarch64/imm_choice_comparison.c: Fix test.
         * gcc.target/aarch64/moveor_imm.c: Add new test.
         * gcc.target/aarch64/pr106583.c: Fix test.

---

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 
578a253d6e0e133e19592553fc873b3e73f9f218..ed5be2b64c9a767d74e9d78415da964c669001aa
 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -5748,6 +5748,26 @@ aarch64_internal_mov_immediate (rtx dest, rtx imm, bool 
generate,
            }
          return 2;
        }
+
+      /* Try 2 bitmask immediates which are xor'd together. */
+      for (i = 0; i < 64; i += 16)
+       {
+         val2 = (val >> i) & mask;
+         val2 |= val2 << 16;
+         val2 |= val2 << 32;
+         if (aarch64_bitmask_imm (val2) && aarch64_bitmask_imm (val ^ val2))
+           break;
+       }
+
+      if (i != 64)
+       {
+         if (generate)
+           {
+             emit_insn (gen_rtx_SET (dest, GEN_INT (val2)));
+             emit_insn (gen_xordi3 (dest, dest, GEN_INT (val ^ val2)));
+           }
+         return 2;
+       }
      }
  
    /* Try a bitmask plus 2 movk to generate the immediate in 3 instructions.  */
diff --git a/gcc/testsuite/gcc.target/aarch64/imm_choice_comparison.c 
b/gcc/testsuite/gcc.target/aarch64/imm_choice_comparison.c
index 
ebc44d6dbc7287d907603d77d7b54496de177c4b..2434ca380ca2cad3e1e4181deeaad680f518b866
 100644
--- a/gcc/testsuite/gcc.target/aarch64/imm_choice_comparison.c
+++ b/gcc/testsuite/gcc.target/aarch64/imm_choice_comparison.c
@@ -6,7 +6,7 @@
  int
  foo (long long x)
  {
-  return x <= 0x1999999999999998;
+  return x <= 0x0000999999999998;
  }
  
  int
diff --git a/gcc/testsuite/gcc.target/aarch64/moveor_imm.c 
b/gcc/testsuite/gcc.target/aarch64/moveor_imm.c
new file mode 100644
index 
0000000000000000000000000000000000000000..5f4997b50398fdda5924610959e0c54967ad0735
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/moveor_imm.c
@@ -0,0 +1,31 @@
+/* { dg-do assemble } */
+/* { dg-options "-O2 --save-temps" } */
+
+long f1 (void)
+{
+  return 0x2aaaaaaaaaaaaaab;
+}
+
+long f2 (void)
+{
+  return 0x10f0f0f0f0f0f0f1;
+}
+
+long f3 (void)
+{
+  return 0xccccccccccccccd;
+}
+
+long f4 (void)
+{
+  return 0x1999999999999998;
+}
+
+long f5 (void)
+{
+  return 0x3f3333333f333333;
+}
+
+/* { dg-final { scan-assembler-not {\tmovk\t} } } */
+/* { dg-final { scan-assembler-times {\tmov\t} 5 } } */
+/* { dg-final { scan-assembler-times {\teor\t} 5 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/pr106583.c 
b/gcc/testsuite/gcc.target/aarch64/pr106583.c
index 
0f931580817d78dc1cc58f03b251bd21bec71f59..79ada5160ce059d66eeaee407ca02488b2a1f114
 100644
--- a/gcc/testsuite/gcc.target/aarch64/pr106583.c
+++ b/gcc/testsuite/gcc.target/aarch64/pr106583.c
@@ -3,7 +3,7 @@
  
  long f1 (void)
  {
-  return 0x7efefefefefefeff;
+  return 0x75fefefefefefeff;
  }
  
  long f2 (void)


I think the tests should be converted to use check-function-bodies, 
rather than scanning for counts on the entire file.  It makes it far 
more obvious what's changed if a test starts to fail.  The functions are 
all trivial, so the test can be quite precise.

Otherwise, this LGTM.

R.