i386: Support wide immediate constants in STV.

This patch provides more accurate costs/gains for (wide) immediate
constants in STV, suitably adjusting the costs/gains when the highpart
and lowpart words are the same.

2024-08-28  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/i386/i386-features.cc (timode_immed_const_gain): New
	function to determine the gain/cost on a CONST_WIDE_INT.
	(timode_scalar_chain::compute_convert_gain): Fix whitespace.
	<case CONST_WIDE_INT>: Provide more accurate estimates using
	timode_immed_const_gain.
	<case AND>: Handle CONSTANT_SCALAR_INT_P (src).

diff --git a/gcc/config/i386/i386-features.cc b/gcc/config/i386/i386-features.cc
index ca902ecf0de578f0accf61b0088154880f4098e7..c09a5c73a8e39f0691f32b6ad0772adc58e7085a 100644 (file)
--- a/gcc/config/i386/i386-features.cc
+++ b/gcc/config/i386/i386-features.cc
@@ -1503,6 +1503,23 @@ general_scalar_chain::convert_insn (rtx_insn *insn)
   df_insn_rescan (insn);
 }
 
+/* Helper function to compute gain for loading an immediate constant.
+   Typically, two movabsq for TImode vs. vmovdqa for V1TImode, but
+   with numerous special cases.  */
+
+static int
+timode_immed_const_gain (rtx cst)
+{
+  /* movabsq vs. movabsq+vmovq+vunpacklqdq.  */
+  if (CONST_WIDE_INT_P (cst)
+      && CONST_WIDE_INT_NUNITS (cst) == 2
+      && CONST_WIDE_INT_ELT (cst, 0) == CONST_WIDE_INT_ELT (cst, 1))
+    return optimize_insn_for_size_p () ? -COSTS_N_BYTES (9)
+                                      : -COSTS_N_INSNS (2);
+  /* 2x movabsq ~ vmovdqa.  */
+  return 0;
+}
+
 /* Compute a gain for chain conversion.  */
 
 int
@@ -1549,7 +1566,14 @@ timode_scalar_chain::compute_convert_gain ()
        case CONST_INT:
          if (MEM_P (dst)
              && standard_sse_constant_p (src, V1TImode))
-           igain = optimize_insn_for_size_p() ? COSTS_N_BYTES (11) : 1;
+           igain = optimize_insn_for_size_p () ? COSTS_N_BYTES (11) : 1;
+         break;
+
+       case CONST_WIDE_INT:
+         /* 2 x mov vs. vmovdqa.  */
+         if (MEM_P (dst))
+           igain = optimize_insn_for_size_p () ? COSTS_N_BYTES (3)
+                                               : COSTS_N_INSNS (1);
          break;
 
        case NOT:
@@ -1562,6 +1586,8 @@ timode_scalar_chain::compute_convert_gain ()
        case IOR:
          if (!MEM_P (dst))
            igain = COSTS_N_INSNS (1);
+         if (CONST_SCALAR_INT_P (XEXP (src, 1)))
+           igain += timode_immed_const_gain (XEXP (src, 1));
          break;
 
        case ASHIFT: