rs6000: Load high and low part of 64bit constant independently

Compare with previous version, this patch updates the comments only.
https://gcc.gnu.org/pipermail/gcc-patches/2022-December/608293.html

For a complicate 64bit constant, below is one instruction-sequence to
build:
	lis 9,0x800a
	ori 9,9,0xabcd
	sldi 9,9,32
	oris 9,9,0xc167
	ori 9,9,0xfa16

while we can also use below sequence to build:
	lis 9,0xc167
	lis 10,0x800a
	ori 9,9,0xfa16
	ori 10,10,0xabcd
	rldimi 9,10,32,0
This sequence is using 2 registers to build high and low part firstly,
and then merge them.

In parallel aspect, this sequence would be faster. (Ofcause, using 1 more
register with potential register pressure).

The instruction sequence with two registers for parallel version can be
generated only if can_create_pseudo_p.  Otherwise, the one register
sequence is generated.

gcc/ChangeLog:

	* config/rs6000/rs6000.cc (rs6000_emit_set_long_const): Generate
	more parallel code if can_create_pseudo_p.

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/parall_5insn_const.c: New test.

diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index 6debf0f63ffece672645a4a26274af3846af834d..3f129ea37d2f6055b76fefde4e792ac47465287f 100644 (file)
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -10385,19 +10385,34 @@ rs6000_emit_set_long_const (rtx dest, HOST_WIDE_INT c)
     }
   else
     {
-      temp = !can_create_pseudo_p () ? dest : gen_reg_rtx (DImode);
-
-      emit_move_insn (temp, GEN_INT (sext_hwi (ud4 << 16, 32)));
-      if (ud3 != 0)
-       emit_move_insn (temp, gen_rtx_IOR (DImode, temp, GEN_INT (ud3)));
+      if (can_create_pseudo_p ())
+       {
+         /* lis HIGH,UD4 ; ori HIGH,UD3 ;
+            lis LOW,UD2 ; ori LOW,UD1 ; rldimi LOW,HIGH,32,0.  */
+         rtx high = gen_reg_rtx (DImode);
+         rtx low = gen_reg_rtx (DImode);
+         HOST_WIDE_INT num = (ud2 << 16) | ud1;
+         rs6000_emit_set_long_const (low, sext_hwi (num, 32));
+         num = (ud4 << 16) | ud3;
+         rs6000_emit_set_long_const (high, sext_hwi (num, 32));
+         emit_insn (gen_rotldi3_insert_3 (dest, high, GEN_INT (32), low,
+                                          GEN_INT (0xffffffff)));
+       }
+      else
+       {
+         /* lis DEST,UD4 ; ori DEST,UD3 ; rotl DEST,32 ;
+            oris DEST,UD2 ; ori DEST,UD1.  */
+         emit_move_insn (dest, GEN_INT (sext_hwi (ud4 << 16, 32)));
+         if (ud3 != 0)
+           emit_move_insn (dest, gen_rtx_IOR (DImode, dest, GEN_INT (ud3)));
 
-      emit_move_insn (ud2 != 0 || ud1 != 0 ? temp : dest,
-                     gen_rtx_ASHIFT (DImode, temp, GEN_INT (32)));
-      if (ud2 != 0)
-       emit_move_insn (ud1 != 0 ? temp : dest,
-                       gen_rtx_IOR (DImode, temp, GEN_INT (ud2 << 16)));
-      if (ud1 != 0)
-       emit_move_insn (dest, gen_rtx_IOR (DImode, temp, GEN_INT (ud1)));
+         emit_move_insn (dest, gen_rtx_ASHIFT (DImode, dest, GEN_INT (32)));
+         if (ud2 != 0)
+           emit_move_insn (dest,
+                           gen_rtx_IOR (DImode, dest, GEN_INT (ud2 << 16)));
+         if (ud1 != 0)
+           emit_move_insn (dest, gen_rtx_IOR (DImode, dest, GEN_INT (ud1)));
+       }
     }
 }
 

diff --git a/gcc/testsuite/gcc.target/powerpc/parall_5insn_const.c b/gcc/testsuite/gcc.target/powerpc/parall_5insn_const.c
new file mode 100644 (file)
index 0000000..e3a9a72
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/parall_5insn_const.c
@@ -0,0 +1,27 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -mno-prefixed -save-temps" } */
+/* { dg-require-effective-target has_arch_ppc64 } */
+
+/* { dg-final { scan-assembler-times {\mlis\M} 4 } } */
+/* { dg-final { scan-assembler-times {\mori\M} 4 } } */
+/* { dg-final { scan-assembler-times {\mrldimi\M} 2 } } */
+
+void __attribute__ ((noinline)) foo (unsigned long long *a)
+{
+  /* 2 lis + 2 ori + 1 rldimi for each constant.  */
+  *a++ = 0x800aabcdc167fa16ULL;
+  *a++ = 0x7543a876867f616ULL;
+}
+
+long long A[] = {0x800aabcdc167fa16ULL, 0x7543a876867f616ULL};
+int
+main ()
+{
+  long long res[2];
+
+  foo (res);
+  if (__builtin_memcmp (res, A, sizeof (res)) != 0)
+    __builtin_abort ();
+
+  return 0;
+}