From: Andrew Pinski <apinski@marvell.com>
Date: Thu, 21 Sep 2023 03:05:17 +0000 (+0000)
Subject: PHIOPT: Fix minmax_replacement for three way
X-Git-Tag: basepoints/gcc-15~5860
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=68fa82e2d8f868a233103102dff2449a416bc566;p=thirdparty%2Fgcc.git

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 --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 000000000000..b68d5989eaca
--- /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 3835d25d08c4..312a6f9082b6 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;