Patchwork Unshare constants in the constant pool (PR target/42894)

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Submitter Jakub Jelinek
Date Jan. 26, 2011, 7:37 p.m.
Message ID <20110126193731.GK2724@tyan-ft48-01.lab.bos.redhat.com>
Download mbox | patch
Permalink /patch/80544/
State New
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Comments

Jakub Jelinek - Jan. 26, 2011, 7:37 p.m.
Hi!

As discussed in the PR, if a non-shareable constant is force_const_mem
and the original expression is used elsewhere in the IL (e.g. in REG_EQUAL
or REG_EQUIV note), unshare_all_rtl doesn't unshare it, but modification of
the IL might result in changes of the constant in theory and if
avoid_constant_pool_reference result is then pushed somewhere else into the
IL, we get RTL sharing errors (as on arm on this testcase).

Bootstrapped/regtested on x86_64-linux and i686-linux, ok if it passes
bootstrap/regtest also on arm?

2011-01-26  Jakub Jelinek  <jakub@redhat.com>

	PR target/42894
	* varasm.c (force_const_mem): Store copy of x in desc->constant
	instead of x itself.

	* gcc.dg/tls/pr42894.c: New test.


	Jakub
Jeff Law - Jan. 27, 2011, 1:29 a.m.
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On 01/26/11 12:37, Jakub Jelinek wrote:
> Hi!
> 
> As discussed in the PR, if a non-shareable constant is force_const_mem
> and the original expression is used elsewhere in the IL (e.g. in REG_EQUAL
> or REG_EQUIV note), unshare_all_rtl doesn't unshare it, but modification of
> the IL might result in changes of the constant in theory and if
> avoid_constant_pool_reference result is then pushed somewhere else into the
> IL, we get RTL sharing errors (as on arm on this testcase).
Well, one could easily argue that using the original expression in the
REG_EQUAL note is incorrect as well.  In fact, looking over all the
calls to set_unique_reg_note shows that most either copy the value or
generate a new one.

I think that means we actually want both the varasm.c and the expr.c
change to avoid incorrect sharing.

jeff

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Jakub Jelinek - Jan. 27, 2011, 8:48 a.m.
On Wed, Jan 26, 2011 at 06:29:25PM -0700, Jeff Law wrote:
> > As discussed in the PR, if a non-shareable constant is force_const_mem
> > and the original expression is used elsewhere in the IL (e.g. in REG_EQUAL
> > or REG_EQUIV note), unshare_all_rtl doesn't unshare it, but modification of
> > the IL might result in changes of the constant in theory and if
> > avoid_constant_pool_reference result is then pushed somewhere else into the
> > IL, we get RTL sharing errors (as on arm on this testcase).
> Well, one could easily argue that using the original expression in the
> REG_EQUAL note is incorrect as well.  In fact, looking over all the
> calls to set_unique_reg_note shows that most either copy the value or
> generate a new one.
> 
> I think that means we actually want both the varasm.c and the expr.c
> change to avoid incorrect sharing.

I think the reason why most of the set_unique_reg_note calls copy_rtx
is that the pattern is usually kept in the insn (or in some other insn).
In the emit_move_insn case it specifically tests that the pattern is not
there (well, some weird target could embed it in some unspec or something),
the reason I changed force_const_mem was to deal with any other uses of
force_const_mem.

But I guess if you strongly prefer to have it in both places I can test a
patch.

	Jakub

Patch

--- gcc/varasm.c.jj	2011-01-25 12:58:41.000000000 +0100
+++ gcc/varasm.c	2011-01-26 14:07:50.635389932 +0100
@@ -3518,7 +3518,7 @@  force_const_mem (enum machine_mode mode,
   pool->offset &= ~ ((align / BITS_PER_UNIT) - 1);
 
   desc->next = NULL;
-  desc->constant = tmp.constant;
+  desc->constant = copy_rtx (tmp.constant);
   desc->offset = pool->offset;
   desc->hash = hash;
   desc->mode = mode;
--- gcc/testsuite/gcc.dg/tls/pr42894.c.jj	2011-01-26 16:29:13.765389223 +0100
+++ gcc/testsuite/gcc.dg/tls/pr42894.c	2011-01-26 16:31:46.830433380 +0100
@@ -0,0 +1,12 @@ 
+/* PR target/42894 */
+/* { dg-do compile } */
+/* { dg-options "-march=armv5te -mthumb" { target arm*-*-* } } */
+/* { dg-require-effective-target tls } */
+
+extern __thread int t;
+
+void
+foo (int a)
+{
+  t = a;
+}