Patchwork [mips,testsuite] Fix gcc.target/mips/octeon-bbit-2.c for -Os

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Submitter Richard Sandiford
Date Dec. 10, 2012, 8:27 p.m.
Message ID <87pq2hy7o8.fsf@talisman.default>
Download mbox | patch
Permalink /patch/205023/
State New
Headers show

Comments

Richard Sandiford - Dec. 10, 2012, 8:27 p.m.
Sorry for the extra-long delay on this one.

"Steve Ellcey " <sellcey@mips.com> writes:
> The gcc.target/octeon-bbit-2.c is failing with -Os because that optimization
> level does not do whichever optimization it is that results in a bbit instead
> of a bbit[01]l.  I would like to skip this test for -Os the way it already gets
> skipped for -O0.

The point of the test is that BBIT[01]L doesn't exist; there aren't any
branch-likely variants of BBIT[01].  So we wanted to check that we could
still use branch-likely instructions for g(), but wouldn't ever generate
the invalid BBIT[01]L for the similarly-structured f().

The problem is that:

  int s = 0;
  for (; i & 1; i++)
    s += i;
  return s;

isn't a very direct way of encouraging branch-likely instructions,
because it requires the i & 1 test to be duplicated.  As you say,
we legimately don't do that for -Os.  A sufficiently fancy gimple
optimiser could also figure out that the loop iterates at most once
and replace the loop with a non-iterating structure.

The patch below uses a form that doesn't require any code duplication
and which should be a bit more future-proof.  Tested on mips64-linux-gnu
and applied.

Richard


gcc/testsuite/
	* gcc.target/mips/octeon-bbit-2.c: Restructure loops so that no
	code duplication is required.  Allow BNE to appear.

Patch

Index: gcc/testsuite/gcc.target/mips/octeon-bbit-2.c
===================================================================
--- gcc/testsuite/gcc.target/mips/octeon-bbit-2.c	2012-08-27 17:27:13.000000000 +0100
+++ gcc/testsuite/gcc.target/mips/octeon-bbit-2.c	2012-10-08 21:23:53.416540290 +0100
@@ -4,22 +4,21 @@ 
 /* { dg-final { scan-assembler "\tbbit\[01\]\t" } } */
 /* { dg-final { scan-assembler-not "\tbbit\[01\]l\t" } } */
 /* { dg-final { scan-assembler "\tbnel\t" } } */
-/* { dg-final { scan-assembler-not "\tbne\t" } } */
 
 NOMIPS16 int
-f (int n, int i)
+f (int *a, int *b)
 {
-  int s = 0;
-  for (; i & 1; i++)
-    s += i;
-  return s;
+  do
+    if (__builtin_expect (*a & 1, 1))
+      *a = 0;
+  while (++a < b);
 }
 
 NOMIPS16 int
-g (int n, int i)
+g (int *a, int *b)
 {
-  int s = 0;
-  for (i = 0; i < n; i++)
-    s += i;
-  return s;
+  do
+    if (__builtin_expect (*a == 3, 1))
+      *a = 0;
+  while (++a < b);
 }