Patchwork reload_reg_reaches_end_p fix

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Submitter Bernd Schmidt
Date Sept. 22, 2011, 5:05 p.m.
Message ID <4E7B6AC3.9040800@codesourcery.com>
Download mbox | patch
Permalink /patch/115970/
State New
Headers show

Comments

Bernd Schmidt - Sept. 22, 2011, 5:05 p.m.
This fixes a reload problem found by Tom de Vries while testing another
patch. An analysis of the problem is in PR50249. Essentially, we have
multiple reloads with the same type, for the same operand, feeding each
other and reusing the same register:

Reload 1: reload_in (SI) = (reg/f:SI 10 sl [588])
        BASE_REGS, RELOAD_FOR_OPERAND_ADDRESS (opnum = 0)
        reload_in_reg: (reg/f:SI 10 sl [588])
        reload_reg_rtx: (reg:SI 1 r1)
Reload 2: reload_in (SI) = (mem:SI (reg/f:SI 10 sl [588]))
        LO_REGS, RELOAD_FOR_OPERAND_ADDRESS (opnum = 0), can't combine
    reload_in_reg: (reg:SI 379)
        reload_reg_rtx: (reg:SI 1 r1)

One might wonder why the first reload isn't using
RELOAD_FOR_OPADDR_ADDR. All the reload types are rewritten in
find_reloads and the last stage of that follows this comment:
 /* Scan all the reloads, and check for RELOAD_FOR_OPERAND_ADDRESS reloads.
     If we have more than one, then convert all RELOAD_FOR_OPADDR_ADDR
     reloads to RELOAD_FOR_OPERAND_ADDRESS reloads.

So, presumably this is valid, and it looks like reload_reg_reaches_end
simply does not deal with this case. The following patch just adds a
loop to look for other reloads that look the same in this way. I've
bootstrapped and tested it on i686-linux; Tom has tested a few other
targets (although I'm not totally sure for which gcc version); it
appears to fix some Thumb libstdc++ testsuite failures.

Thoughts? I plan to install this tomorrow or so unless someone sees a
problem.


Bernd
PR rtl-optimization/50249
	* reload1.c (reload_reg_reaches_end_p): Accept a reloadnum argument
	instead of opnum and type.  All callers changed.  Remove useless
	declaration.
	Search forward for other reloads of the same type for the same operand
	using the same register; if any are found, return false.
	(reload_regs_reach_end_p): Same argument changes; all callers changed.

Patch

Index: reload1.c
===================================================================
--- reload1.c	(revision 178583)
+++ reload1.c	(working copy)
@@ -396,7 +396,6 @@  static int reload_reg_free_for_value_p (
 					rtx, rtx, int, int);
 static int free_for_value_p (int, enum machine_mode, int, enum reload_type,
 			     rtx, rtx, int, int);
-static int reload_reg_reaches_end_p (unsigned int, int, enum reload_type);
 static int allocate_reload_reg (struct insn_chain *, int, int);
 static int conflicts_with_override (rtx);
 static void failed_reload (rtx, int);
@@ -5346,19 +5345,37 @@  reload_reg_free_p (unsigned int regno, i
     }
 }
 
-/* Return 1 if the value in reload reg REGNO, as used by a reload
-   needed for the part of the insn specified by OPNUM and TYPE,
-   is still available in REGNO at the end of the insn.
+/* Return 1 if the value in reload reg REGNO, as used by the reload with
+   the number RELOADNUM, is still available in REGNO at the end of the insn.
 
    We can assume that the reload reg was already tested for availability
    at the time it is needed, and we should not check this again,
    in case the reg has already been marked in use.  */
 
 static int
-reload_reg_reaches_end_p (unsigned int regno, int opnum, enum reload_type type)
+reload_reg_reaches_end_p (unsigned int regno, int reloadnum)
 {
+  int opnum = rld[reloadnum].opnum;
+  enum reload_type type = rld[reloadnum].when_needed;
   int i;
 
+  /* See if there is a reload with the same type for this operand, using
+     the same register. This case is not handled by the code below.  */
+  for (i = reloadnum + 1; i < n_reloads; i++)
+    {
+      rtx reg;
+      int nregs;
+
+      if (rld[i].opnum != opnum || rld[i].when_needed != type)
+	continue;
+      reg = rld[i].reg_rtx;
+      if (reg == NULL_RTX)
+	continue;
+      nregs = hard_regno_nregs[REGNO (reg)][GET_MODE (reg)];
+      if (regno >= REGNO (reg) && regno < REGNO (reg) + nregs)
+	return 0;
+    }
+  
   switch (type)
     {
     case RELOAD_OTHER:
@@ -5485,13 +5502,12 @@  reload_reg_reaches_end_p (unsigned int r
    every register in the range [REGNO, REGNO + NREGS).  */
 
 static bool
-reload_regs_reach_end_p (unsigned int regno, int nregs,
-			 int opnum, enum reload_type type)
+reload_regs_reach_end_p (unsigned int regno, int nregs, int reloadnum)
 {
   int i;
 
   for (i = 0; i < nregs; i++)
-    if (!reload_reg_reaches_end_p (regno + i, opnum, type))
+    if (!reload_reg_reaches_end_p (regno + i, reloadnum))
       return false;
   return true;
 }
@@ -8103,8 +8119,7 @@  emit_reload_insns (struct insn_chain *ch
 	  /* For a multi register reload, we need to check if all or part
 	     of the value lives to the end.  */
 	  for (k = 0; k < nr; k++)
-	    if (reload_reg_reaches_end_p (i + k, rld[r].opnum,
-					  rld[r].when_needed))
+	    if (reload_reg_reaches_end_p (i + k, r))
 	      CLEAR_HARD_REG_BIT (reg_reloaded_valid, i + k);
 
 	  /* Maybe the spill reg contains a copy of reload_out.  */
@@ -8135,8 +8150,7 @@  emit_reload_insns (struct insn_chain *ch
 	      mode = GET_MODE (reg);
 	      regno = REGNO (reg);
 	      nregs = hard_regno_nregs[regno][mode];
-	      if (reload_regs_reach_end_p (regno, nregs, rld[r].opnum,
-					   rld[r].when_needed))
+	      if (reload_regs_reach_end_p (regno, nregs, r))
 		{
 		  rtx out = (REG_P (rld[r].out)
 			     ? rld[r].out
@@ -8208,8 +8222,7 @@  emit_reload_insns (struct insn_chain *ch
 	      mode = GET_MODE (reg);
 	      regno = REGNO (reg);
 	      nregs = hard_regno_nregs[regno][mode];
-	      if (reload_regs_reach_end_p (regno, nregs, rld[r].opnum,
-					   rld[r].when_needed))
+	      if (reload_regs_reach_end_p (regno, nregs, r))
 		{
 		  int in_regno;
 		  int in_nregs;