On Feb 4, 2015, Alexandre Oliva <lxol...@fsfla.org> wrote:
> Nevermind, I got the build stuck at vp9_cx_iface on parkes, and on the
> cross compiler at a faster build machine. It gets stuck in the first
> common subexpression elimination optimization pass (cse1) in a partial
> clone of function validate_config. It fails even with -O2.
> I found out that compiling with -fno-cse-follow-jumps in addition to -O3
> or -O2 makes it finish compilation very quickly, presumably at some loss
> of optimization. You might want to use that for now, at least until I
> debug the compiler it properly. That might take a while, though.
For tiny values of a while, fortunately ;-)
This is GCC bug 50380:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50380
The patch associated with that PR is enough to get vp9_cx_iface to
compile, however, there was a subsequent patch that complemented the fix
so as to catch additional similar situations that would loop endlessly.
I enclose both patches below. Building gcc with both ought to fix the
problem and make libvpx (and hopefully iceweasel) buildable.
2011-12-19 Sandra Loosemore <san...@codesourcery.com>
From: sandra <sandra@138bc75d-0d04-0410-961f-82ee72b054a4>
Tom de Vries <t...@codesourcery.com>
PR rtl-opt/50380
gcc/
* cse.c (find_comparison_args): Detect fixed point and
bail early.
gcc/testsuite/
* gcc.c-torture/compile/pr50380.c: New testcase.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@182498 138bc75d-0d04-0410-961f-82ee72b054a4
---
gcc/cse.c | 6 ++++++
gcc/testsuite/gcc.c-torture/compile/pr50380.c | 12 ++++++++++++
2 files changed, 18 insertions(+)
create mode 100644 gcc/testsuite/gcc.c-torture/compile/pr50380.c
diff --git a/gcc/cse.c b/gcc/cse.c
index 078977f..7609114 100644
--- a/gcc/cse.c
+++ b/gcc/cse.c
@@ -3054,6 +3054,12 @@ find_comparison_args (enum rtx_code code, rtx *parg1, rtx *parg2,
if (! exp_equiv_p (p->exp, p->exp, 1, false))
continue;
+ /* If it's the same comparison we're already looking at, skip it. */
+ if (COMPARISON_P (p->exp)
+ && XEXP (p->exp, 0) == arg1
+ && XEXP (p->exp, 1) == arg2)
+ continue;
+
if (GET_CODE (p->exp) == COMPARE
/* Another possibility is that this machine has a compare insn
that includes the comparison code. In that case, ARG1 would
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr50380.c b/gcc/testsuite/gcc.c-torture/compile/pr50380.c
new file mode 100644
index 0000000..ffd0442
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr50380.c
@@ -0,0 +1,12 @@
+/* This test used to get stuck in an infinite loop in find_comparison_args
+ when compiling for MIPS at -O2. */
+
+__attribute__ ((__noreturn__)) extern void fail (void);
+
+char x;
+
+void foo (const unsigned char y)
+{
+ ((void) (__builtin_expect((!! y == y), 1) ? 0 : (fail (), 0)));
+ x = ! y;
+}
2012-07-26 Andrew Jenner <and...@codesourcery.com>
From: sandra <sandra@138bc75d-0d04-0410-961f-82ee72b054a4>
Sandra Loosemore <san...@codesourcery.com>
gcc/
* cse.c (find_comparison_args): Check for cycles of any length.
gcc/testsuite/
* gcc.c-torture/compile/pr50380.c: Add code to cause cycle of length 2.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@189896 138bc75d-0d04-0410-961f-82ee72b054a4
---
gcc/cse.c | 23 +++++++++++++++++------
gcc/testsuite/gcc.c-torture/compile/pr50380.c | 16 +++++++++++++---
2 files changed, 30 insertions(+), 9 deletions(-)
diff --git a/gcc/cse.c b/gcc/cse.c
index 7609114..8b32350 100644
--- a/gcc/cse.c
+++ b/gcc/cse.c
@@ -45,6 +45,7 @@ along with GCC; see the file COPYING3. If not see
#include "tree-pass.h"
#include "df.h"
#include "dbgcnt.h"
+#include "pointer-set.h"
/* The basic idea of common subexpression elimination is to go
through the code, keeping a record of expressions that would
@@ -2966,6 +2967,9 @@ find_comparison_args (enum rtx_code code, rtx *parg1, rtx *parg2,
enum machine_mode *pmode1, enum machine_mode *pmode2)
{
rtx arg1, arg2;
+ struct pointer_set_t *visited = NULL;
+ /* Set nonzero when we find something of interest. */
+ rtx x = NULL;
arg1 = *parg1, arg2 = *parg2;
@@ -2973,11 +2977,18 @@ find_comparison_args (enum rtx_code code, rtx *parg1, rtx *parg2,
while (arg2 == CONST0_RTX (GET_MODE (arg1)))
{
- /* Set nonzero when we find something of interest. */
- rtx x = 0;
int reverse_code = 0;
struct table_elt *p = 0;
+ /* Remember state from previous iteration. */
+ if (x)
+ {
+ if (!visited)
+ visited = pointer_set_create ();
+ pointer_set_insert (visited, x);
+ x = 0;
+ }
+
/* If arg1 is a COMPARE, extract the comparison arguments from it.
On machines with CC0, this is the only case that can occur, since
fold_rtx will return the COMPARE or item being compared with zero
@@ -3054,10 +3065,8 @@ find_comparison_args (enum rtx_code code, rtx *parg1, rtx *parg2,
if (! exp_equiv_p (p->exp, p->exp, 1, false))
continue;
- /* If it's the same comparison we're already looking at, skip it. */
- if (COMPARISON_P (p->exp)
- && XEXP (p->exp, 0) == arg1
- && XEXP (p->exp, 1) == arg2)
+ /* If it's a comparison we've used before, skip it. */
+ if (visited && pointer_set_contains (visited, p->exp))
continue;
if (GET_CODE (p->exp) == COMPARE
@@ -3146,6 +3155,8 @@ find_comparison_args (enum rtx_code code, rtx *parg1, rtx *parg2,
*pmode1 = GET_MODE (arg1), *pmode2 = GET_MODE (arg2);
*parg1 = fold_rtx (arg1, 0), *parg2 = fold_rtx (arg2, 0);
+ if (visited)
+ pointer_set_destroy (visited);
return code;
}
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr50380.c b/gcc/testsuite/gcc.c-torture/compile/pr50380.c
index ffd0442..3f03cbb 100644
--- a/gcc/testsuite/gcc.c-torture/compile/pr50380.c
+++ b/gcc/testsuite/gcc.c-torture/compile/pr50380.c
@@ -1,12 +1,22 @@
-/* This test used to get stuck in an infinite loop in find_comparison_args
- when compiling for MIPS at -O2. */
-
__attribute__ ((__noreturn__)) extern void fail (void);
char x;
+/* This used to get stuck in an infinite loop in find_comparison_args
+ when compiling this function for MIPS at -O2. */
+
void foo (const unsigned char y)
{
((void) (__builtin_expect((!! y == y), 1) ? 0 : (fail (), 0)));
x = ! y;
}
+
+/* This used to similarly get stuck when compiling for PowerPC at -O2. */
+
+int foo2 (int arg)
+{
+ if (arg != !arg)
+ fail ();
+ if (arg)
+ fail ();
+}
--
Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/ FSF Latin America board member
Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer
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