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* [gcc r14-4279] PHIOPT: Fix minmax_replacement for three way
@ 2023-09-26 14:55 Andrew Pinski
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From: Andrew Pinski @ 2023-09-26 14:55 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:68fa82e2d8f868a233103102dff2449a416bc566
commit r14-4279-g68fa82e2d8f868a233103102dff2449a416bc566
Author: Andrew Pinski <apinski@marvell.com>
Date: Thu Sep 21 03:05:17 2023 +0000
PHIOPT: Fix minmax_replacement for three way
So when diamond bb support was added to minmax_replacement in r13-1950-g9bb19e143cfe,
the code was not expecting the alt_middle_bb not to exist if it was empty (for threeway_p).
So when factor_out_conditional_conversion was used to factor out conversions, it turns out
the assumption for alt_middle_bb to be wrong and we ended up with threeway_p being true but
having middle_bb being empty but alt_middle_bb not being empty which causes wrong code in
many cases.
This patch fixes the issue by adding a test for the 2 cases where the assumption on
threeway_p case having the other bb being empty.
Changes made:
v2: Fix test for `(a <= u) b = MAX(a, d) else b = u`.
Note my plan for GCC 15 is remove minmax_replacement as match.pd will catch all cases
at that point.
OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.
PR tree-optimization/111469
gcc/ChangeLog:
* tree-ssa-phiopt.cc (minmax_replacement): Fix
the assumption for the `non-diamond` handling cases
of diamond code.
gcc/testsuite/ChangeLog:
* gcc.c-torture/execute/pr111469-1.c: New test.
Diff:
---
gcc/testsuite/gcc.c-torture/execute/pr111469-1.c | 38 ++++++++++++++++++++++++
gcc/tree-ssa-phiopt.cc | 9 ++++--
2 files changed, 45 insertions(+), 2 deletions(-)
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr111469-1.c b/gcc/testsuite/gcc.c-torture/execute/pr111469-1.c
new file mode 100644
index 00000000000..b68d5989eac
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr111469-1.c
@@ -0,0 +1,38 @@
+/* PR tree-optimization/111469 */
+
+long f;
+char *g;
+__attribute__((noinline))
+char o() {
+ char l;
+ while (f)
+ ;
+ l = *g;
+ return l;
+}
+
+/* factor_out_conditional_conversion is able to remove the casts
+ from the 2 bbs (correctly)
+ but then minmax_replacement should not optimize this to a MIN_EXPR
+ as o has side effects. */
+
+__attribute__((noinline))
+unsigned short gg(unsigned short a, unsigned short b)
+{
+ short d;
+ if (a > b)
+ {
+ d= b;
+ }
+ else
+ {
+ o();
+ d = a;
+ }
+ return d;
+}
+
+int main(void)
+{
+ gg(3, 2);
+}
diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index 3835d25d08c..312a6f9082b 100644
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -1823,7 +1823,9 @@ minmax_replacement (basic_block cond_bb, basic_block middle_bb, basic_block alt_
arg_false = arg0;
}
- if (empty_block_p (middle_bb))
+ if (empty_block_p (middle_bb)
+ && (!threeway_p
+ || empty_block_p (alt_middle_bb)))
{
if ((operand_equal_for_phi_arg_p (arg_true, smaller)
|| (alt_smaller
@@ -2006,7 +2008,8 @@ minmax_replacement (basic_block cond_bb, basic_block middle_bb, basic_block alt_
return true;
}
- else
+ else if (!threeway_p
+ || empty_block_p (alt_middle_bb))
{
/* Recognize the following case, assuming d <= u:
@@ -2182,6 +2185,8 @@ minmax_replacement (basic_block cond_bb, basic_block middle_bb, basic_block alt_
SSA_OP_DEF));
gsi_move_before (&gsi_from, &gsi);
}
+ else
+ return false;
/* Emit the statement to compute min/max. */
gimple_seq stmts = NULL;
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