[Apologies if this is a duplicate, I'm unsure if my previous mail was
delivered]
On 01/07/19 12:38, Richard Biener wrote:
On Mon, Jul 1, 2019 at 1:22 PM Joern Wolfgang Rennecke
<joern.renne...@riscy-ip.com> wrote:
The heuristic introduced for PR71016 prevents recognizing a max / min
combo like it is used for
saturation when followed by a conversion.
The attached patch refines the heuristic to allow this case. Regression
tested on x86_64-pc-linux-gnu .
Few style nits:
...
also please check that 'lhs' is equal to gimple_assing_rhs1 (arg0_def_stmt)
otherwise you'd also allow MIN/MAX unrelated to the conversion detected.
Like the attached patch?
On x86 I see the MIN_EXPR is already detected by GENERIC folding,
I wonder if that is required or if we can handle the case without in one
phiopt pass invocation as well.
tree_ssa_phiopt_worker is supposed to handle this by handling nested
COND_EXPRs
from the inside out:
/* Search every basic block for COND_EXPR we may be able to optimize.
We walk the blocks in order that guarantees that a block with
a single predecessor is processed before the predecessor.
This ensures that we collapse inner ifs before visiting the
outer ones, and also that we do not try to visit a removed
block. */
bb_order = single_pred_before_succ_order ();
However, I have no idea how to construct a testcase for this with the
gimple folding in place.
#define SAT(x) (x < 0 ? 0 : (x > 255 ? 255 : x))
void
foo (unsigned char *p, int i, int m)
{
*p = (m > SAT (i) ? m : SAT (i));
}
or the equivalent for MIN_EXPR, *.c.004.original already has only one
conditional left.
2019-07-01 Joern Rennecke <joern.renne...@riscy-ip.com>
PR middle-end/66726
* tree-ssa-phiopt.c (factor_out_conditional_conversion):
Tune heuristic from PR71016 to allow MIN / MAX.
* testsuite/gcc.dg/tree-ssa/pr66726-4.c: New testcase.
Index: tree-ssa-phiopt.c
===================================================================
--- tree-ssa-phiopt.c (revision 272846)
+++ tree-ssa-phiopt.c (working copy)
@@ -504,7 +504,25 @@ factor_out_conditional_conversion (edge
gsi = gsi_for_stmt (arg0_def_stmt);
gsi_prev_nondebug (&gsi);
if (!gsi_end_p (gsi))
- return NULL;
+ {
+ if (gassign *assign
+ = dyn_cast <gassign *> (gsi_stmt (gsi)))
+ {
+ tree lhs = gimple_assign_lhs (assign);
+ enum tree_code ass_code
+ = gimple_assign_rhs_code (assign);
+ if (ass_code != MAX_EXPR && ass_code != MIN_EXPR)
+ return NULL;
+ if (!operand_equal_p
+ (lhs, gimple_assign_rhs1 (arg0_def_stmt), 0))
+ return NULL;
+ gsi_prev_nondebug (&gsi);
+ if (!gsi_end_p (gsi))
+ return NULL;
+ }
+ else
+ return NULL;
+ }
gsi = gsi_for_stmt (arg0_def_stmt);
gsi_next_nondebug (&gsi);
if (!gsi_end_p (gsi))
Index: testsuite/gcc.dg/tree-ssa/pr66726-4.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/pr66726-4.c (nonexistent)
+++ testsuite/gcc.dg/tree-ssa/pr66726-4.c (working copy)
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-phiopt1-details" } */
+
+#define SAT(x) (x < 0 ? 0 : (x > 255 ? 255 : x))
+
+void
+foo (unsigned char *p, int i)
+{
+ *p = SAT (i);
+}
+
+/* { dg-final { scan-tree-dump-times "COND_EXPR .*and PHI .*converted to
straightline code" 1 "phiopt1" } } */
