[PATCH] tree-optimization/96579 - another special-operands fix in reassoc

Richard Biener rguenther@suse.de
Thu Aug 27 08:04:24 GMT 2020


This makes sure to put special-ops expanded rhs left where
expression rewrite expects it.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

2020-08-27  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/96579
	* tree-ssa-reassoc.c (linearize_expr_tree): If we expand
	rhs via special ops make sure to swap operands.

	* gcc.dg/pr96579.c: New testcase.
---
 gcc/testsuite/gcc.dg/pr96579.c |  4 ++++
 gcc/tree-ssa-reassoc.c         | 13 +++++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/pr96579.c

diff --git a/gcc/testsuite/gcc.dg/pr96579.c b/gcc/testsuite/gcc.dg/pr96579.c
new file mode 100644
index 00000000000..49fdcb40359
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr96579.c
@@ -0,0 +1,4 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fno-tree-forwprop -ffast-math -fno-tree-vrp" } */
+
+#include "pr96370.c"
diff --git a/gcc/tree-ssa-reassoc.c b/gcc/tree-ssa-reassoc.c
index fed463b0350..a5f5d52edab 100644
--- a/gcc/tree-ssa-reassoc.c
+++ b/gcc/tree-ssa-reassoc.c
@@ -5651,13 +5651,20 @@ linearize_expr_tree (vec<operand_entry *> *ops, gimple *stmt,
 
       if (!binrhsisreassoc)
 	{
-	  if (!try_special_add_to_ops (ops, rhscode, binrhs, binrhsdef))
+	  bool swap = false;
+	  if (try_special_add_to_ops (ops, rhscode, binrhs, binrhsdef))
+	    /* If we add ops for the rhs we expect to be able to recurse
+	       to it via the lhs during expression rewrite so swap
+	       operands.  */
+	    swap = true;
+	  else
 	    add_to_ops_vec (ops, binrhs);
 
 	  if (!try_special_add_to_ops (ops, rhscode, binlhs, binlhsdef))
 	    add_to_ops_vec (ops, binlhs);
 
-	  return;
+	  if (!swap)
+	    return;
 	}
 
       if (dump_file && (dump_flags & TDF_DETAILS))
@@ -5676,6 +5683,8 @@ linearize_expr_tree (vec<operand_entry *> *ops, gimple *stmt,
 	  fprintf (dump_file, " is now ");
 	  print_gimple_stmt (dump_file, stmt, 0);
 	}
+      if (!binrhsisreassoc)
+	return;
 
       /* We want to make it so the lhs is always the reassociative op,
 	 so swap.  */
-- 
2.26.2


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