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Re: PR rtl-optimization/46603


> Thanks!

You're welcome.  I have also installed the attached patch which makes minor 
tweaks and fixes various issues in comments which have bugged me for years, 
the most glaring one being:

     Similar issue for (SUBREG:M1 (REG:M2 ...) ...) for a hard register R where
     either M1 is not valid for R or M2 is wider than a word but we only
     need one word to store an M2-sized quantity in R.

which seems to be hinting at some relativistic effect on the size of M2...

No functional changes, tested on i586-suse-linux, applied on the mainline.


2011-10-26  Eric Botcazou  <ebotcazou@adacore.com>

	* reload.c (reload_inner_reg_of_subreg): Change type of return value
	and type of OUTPUT parameter to bool and adjust.  Document MODE and
	OUTPUT parameters.  Use HARD_REGISTER_P.  Reorder final condition
	and improve associated comment.
	(push_reload): Clarify and update comments about reloading of subregs.
	Adjust calls to reload_inner_reg_of_subreg.  Compute the class upfront
	for the reloading of subregs in the out case as well.


-- 
Eric Botcazou
Index: reload.c
===================================================================
--- reload.c	(revision 180457)
+++ reload.c	(working copy)
@@ -256,7 +256,6 @@ static int push_secondary_reload (int, r
 				  enum insn_code *, secondary_reload_info *);
 static enum reg_class find_valid_class (enum machine_mode, enum machine_mode,
 					int, unsigned int);
-static int reload_inner_reg_of_subreg (rtx, enum machine_mode, int);
 static void push_replacement (rtx *, int, enum machine_mode);
 static void dup_replacements (rtx *, rtx *);
 static void combine_reloads (void);
@@ -791,39 +790,39 @@ find_reusable_reload (rtx *p_in, rtx out
   return n_reloads;
 }
 
-/* Return nonzero if X is a SUBREG which will require reloading of its
-   SUBREG_REG expression.  */
+/* Return true if X is a SUBREG that will need reloading of its SUBREG_REG
+   expression.  MODE is the mode that X will be used in.  OUTPUT is true if
+   the function is invoked for the output part of an enclosing reload.  */
 
-static int
-reload_inner_reg_of_subreg (rtx x, enum machine_mode mode, int output)
+static bool
+reload_inner_reg_of_subreg (rtx x, enum machine_mode mode, bool output)
 {
   rtx inner;
 
   /* Only SUBREGs are problematical.  */
   if (GET_CODE (x) != SUBREG)
-    return 0;
+    return false;
 
   inner = SUBREG_REG (x);
 
-  /* If INNER is a constant or PLUS, then INNER must be reloaded.  */
+  /* If INNER is a constant or PLUS, then INNER will need reloading.  */
   if (CONSTANT_P (inner) || GET_CODE (inner) == PLUS)
-    return 1;
+    return true;
 
-  /* If INNER is not a hard register, then INNER will not need to
-     be reloaded.  */
-  if (!REG_P (inner)
-      || REGNO (inner) >= FIRST_PSEUDO_REGISTER)
-    return 0;
+  /* If INNER is not a hard register, then INNER will not need reloading.  */
+  if (!(REG_P (inner) && HARD_REGISTER_P (inner)))
+    return false;
 
   /* If INNER is not ok for MODE, then INNER will need reloading.  */
-  if (! HARD_REGNO_MODE_OK (subreg_regno (x), mode))
-    return 1;
+  if (!HARD_REGNO_MODE_OK (subreg_regno (x), mode))
+    return true;
 
-  /* If the outer part is a word or smaller, INNER larger than a
-     word and the number of regs for INNER is not the same as the
-     number of words in INNER, then INNER will need reloading.  */
-  return (GET_MODE_SIZE (mode) <= UNITS_PER_WORD
-	  && output
+  /* If this is for an output, and the outer part is a word or smaller,
+     INNER is larger than a word and the number of registers in INNER is
+     not the same as the number of words in INNER, then INNER will need
+     reloading (with an in-out reload).  */
+  return (output
+	  && GET_MODE_SIZE (mode) <= UNITS_PER_WORD
 	  && GET_MODE_SIZE (GET_MODE (inner)) > UNITS_PER_WORD
 	  && ((GET_MODE_SIZE (GET_MODE (inner)) / UNITS_PER_WORD)
 	      != (int) hard_regno_nregs[REGNO (inner)][GET_MODE (inner)]));
@@ -990,9 +989,9 @@ push_reload (rtx in, rtx out, rtx *inloc
      For machines that extend byte loads, do this for any SUBREG of a pseudo
      where both M1 and M2 are a word or smaller, M1 is wider than M2, and
      M2 is an integral mode that gets extended when loaded.
-     Similar issue for (SUBREG:M1 (REG:M2 ...) ...) for a hard register R where
-     either M1 is not valid for R or M2 is wider than a word but we only
-     need one word to store an M2-sized quantity in R.
+     Similar issue for (SUBREG:M1 (REG:M2 ...) ...) for a hard register R
+     where either M1 is not valid for R or M2 is wider than a word but we
+     only need one register to store an M2-sized quantity in R.
      (However, if OUT is nonzero, we need to reload the reg *and*
      the subreg, so do nothing here, and let following statement handle it.)
 
@@ -1082,17 +1081,16 @@ push_reload (rtx in, rtx out, rtx *inloc
       inmode = GET_MODE (in);
     }
 
-  /* Similar issue for (SUBREG:M1 (REG:M2 ...) ...) for a hard register R where
-     either M1 is not valid for R or M2 is wider than a word but we only
-     need one word to store an M2-sized quantity in R.
+  /* Similar issue for (SUBREG:M1 (REG:M2 ...) ...) for a hard register R
+     where M1 is not valid for R if it was not handled by the code above.
+
+     Similar issue for (SUBREG constant ...) if it was not handled by the
+     code above.  This can happen if SUBREG_BYTE != 0.
 
      However, we must reload the inner reg *as well as* the subreg in
      that case.  */
 
-  /* Similar issue for (SUBREG constant ...) if it was not handled by the
-     code above.  This can happen if SUBREG_BYTE != 0.  */
-
-  if (in != 0 && reload_inner_reg_of_subreg (in, inmode, 0))
+  if (in != 0 && reload_inner_reg_of_subreg (in, inmode, false))
     {
       enum reg_class in_class = rclass;
 
@@ -1168,31 +1166,32 @@ push_reload (rtx in, rtx out, rtx *inloc
       outmode = GET_MODE (out);
     }
 
-  /* Similar issue for (SUBREG:M1 (REG:M2 ...) ...) for a hard register R where
-     either M1 is not valid for R or M2 is wider than a word but we only
-     need one word to store an M2-sized quantity in R.
+  /* Similar issue for (SUBREG:M1 (REG:M2 ...) ...) for a hard register R
+     where either M1 is not valid for R or M2 is wider than a word but we
+     only need one register to store an M2-sized quantity in R.
 
      However, we must reload the inner reg *as well as* the subreg in
-     that case.  In this case, the inner reg is an in-out reload.  */
+     that case and the inner reg is an in-out reload.  */
 
-  if (out != 0 && reload_inner_reg_of_subreg (out, outmode, 1))
+  if (out != 0 && reload_inner_reg_of_subreg (out, outmode, true))
     {
+      enum reg_class in_out_class
+	= find_valid_class (outmode, GET_MODE (SUBREG_REG (out)),
+			    subreg_regno_offset (REGNO (SUBREG_REG (out)),
+						 GET_MODE (SUBREG_REG (out)),
+						 SUBREG_BYTE (out),
+						 GET_MODE (out)),
+			    REGNO (SUBREG_REG (out)));
+
       /* This relies on the fact that emit_reload_insns outputs the
 	 instructions for output reloads of type RELOAD_OTHER in reverse
 	 order of the reloads.  Thus if the outer reload is also of type
 	 RELOAD_OTHER, we are guaranteed that this inner reload will be
 	 output after the outer reload.  */
-      dont_remove_subreg = 1;
       push_reload (SUBREG_REG (out), SUBREG_REG (out), &SUBREG_REG (out),
-		   &SUBREG_REG (out),
-		   find_valid_class (outmode, GET_MODE (SUBREG_REG (out)),
-				     subreg_regno_offset (REGNO (SUBREG_REG (out)),
-							  GET_MODE (SUBREG_REG (out)),
-							  SUBREG_BYTE (out),
-							  GET_MODE (out)),
-				     REGNO (SUBREG_REG (out))),
-		   VOIDmode, VOIDmode, 0, 0,
-		   opnum, RELOAD_OTHER);
+		   &SUBREG_REG (out), in_out_class, VOIDmode, VOIDmode,
+		   0, 0, opnum, RELOAD_OTHER);
+      dont_remove_subreg = 1;
     }
 
   /* If IN appears in OUT, we can't share any input-only reload for IN.  */

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