[i386] Fix couple of issues in large PIC model on x86-64/VxWorks

[i386] Fix couple of issues in large PIC model on x86-64/VxWorks

[Eric Botcazou]

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Hi,

the first issue is that the !gotoff_operand path of legitimize_pic_address in 
large PIC model does not make use of REG when it is available, which breaks 
for thunks because new pseudo-registers can no longer be created.  And the 
second issue is that the system compiler (LLVM) generates @GOTOFF in large 
model even for RTP, so we do the same.

Tested on x86-64/Linux and VxWorks, OK for the mainline?


2021-10-05  Eric Botcazou  <ebotcazou@adacore.com>

	* config/i386/i386.c (legitimize_pic_address): Adjust comment and
	use the REG argument on the CM_LARGE_PIC code path as well.
	* config/i386/predicates.md (gotoff_operand): Do not treat VxWorks
	specially with the large code models.

-- 
Eric Botcazou

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diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index a566d84a61e..a6784c4e9d6 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -11152,7 +11152,7 @@ legitimize_pic_address (rtx orig, rtx reg)
 	new_rtx = gen_rtx_PLUS (Pmode, pic_offset_table_rtx, new_rtx);
     }
   else if ((GET_CODE (addr) == SYMBOL_REF && SYMBOL_REF_TLS_MODEL (addr) == 0)
-	   /* We can't use @GOTOFF for text labels
+	   /* We can't always use @GOTOFF for text labels
 	      on VxWorks, see gotoff_operand.  */
 	   || (TARGET_VXWORKS_RTP && GET_CODE (addr) == LABEL_REF))
     {
@@ -11181,9 +11181,19 @@ legitimize_pic_address (rtx orig, rtx reg)
 	     from the Global Offset Table (@GOT).  */
 	  new_rtx = gen_rtx_UNSPEC (Pmode, gen_rtvec (1, addr), UNSPEC_GOT);
 	  new_rtx = gen_rtx_CONST (Pmode, new_rtx);
+
 	  if (TARGET_64BIT)
-	    new_rtx = force_reg (Pmode, new_rtx);
-	  new_rtx = gen_rtx_PLUS (Pmode, pic_offset_table_rtx, new_rtx);
+	    new_rtx = copy_to_suggested_reg (new_rtx, reg, Pmode);
+
+	  if (reg != 0)
+	    {
+	      gcc_assert (REG_P (reg));
+	      new_rtx = expand_simple_binop (Pmode, PLUS, pic_offset_table_rtx,
+					     new_rtx, reg, 1, OPTAB_DIRECT);
+	    }
+	  else
+	    new_rtx = gen_rtx_PLUS (Pmode, pic_offset_table_rtx, new_rtx);
+
 	  new_rtx = gen_const_mem (Pmode, new_rtx);
 	  set_mem_alias_set (new_rtx, ix86_GOT_alias_set ());
 	}
diff --git a/gcc/config/i386/predicates.md b/gcc/config/i386/predicates.md
index df5acb425d4..af2a573f3dd 100644
--- a/gcc/config/i386/predicates.md
+++ b/gcc/config/i386/predicates.md
@@ -617,9 +617,11 @@
 ;; use @GOTOFF unless we are absolutely sure that the symbol is in the
 ;; same segment as the GOT.  Unfortunately, the flexibility of linker
 ;; scripts means that we can't be sure of that in general, so assume
-;; that @GOTOFF is never valid on VxWorks.
+;; @GOTOFF is not valid on VxWorks, except with the large code model.
 (define_predicate "gotoff_operand"
-  (and (not (match_test "TARGET_VXWORKS_RTP"))
+  (and (ior (not (match_test "TARGET_VXWORKS_RTP"))
+            (match_test "ix86_cmodel == CM_LARGE")
+            (match_test "ix86_cmodel == CM_LARGE_PIC"))
        (match_operand 0 "local_symbolic_operand")))
 
 ;; Test for various thread-local symbols.

Re: [i386] Fix couple of issues in large PIC model on x86-64/VxWorks

[Uros Bizjak]

On Tue, Oct 5, 2021 at 5:50 PM Eric Botcazou via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi,
>
> the first issue is that the !gotoff_operand path of legitimize_pic_address in
> large PIC model does not make use of REG when it is available, which breaks
> for thunks because new pseudo-registers can no longer be created.  And the
> second issue is that the system compiler (LLVM) generates @GOTOFF in large
> model even for RTP, so we do the same.
>
> Tested on x86-64/Linux and VxWorks, OK for the mainline?
>
>
> 2021-10-05  Eric Botcazou  <ebotcazou@adacore.com>
>
>         * config/i386/i386.c (legitimize_pic_address): Adjust comment and
>         use the REG argument on the CM_LARGE_PIC code path as well.
>         * config/i386/predicates.md (gotoff_operand): Do not treat VxWorks
>         specially with the large code models.

LGTM for the generic part, no idea for VxWorks.

Thanks,
Uros.

Re: [i386] Fix couple of issues in large PIC model on x86-64/VxWorks

[Eric Botcazou]

> LGTM for the generic part, no idea for VxWorks.

Thanks.  The VxWorks-specific hunk is needed to make GCC compatible with the 
system compiler on this architecture (LLVM) and I have CCed Olivier.

-- 
Eric Botcazou

Re: [i386] Fix couple of issues in large PIC model on x86-64/VxWorks

[Olivier Hainque]

> On 8 Nov 2021, at 09:27, Eric Botcazou <botcazou@adacore.com> wrote:
> 
>> LGTM for the generic part, no idea for VxWorks.
> 
> Thanks.  The VxWorks-specific hunk is needed to make GCC compatible with the 
> system compiler on this architecture (LLVM) and I have CCed Olivier.

Good for me, thanks Eric!