Hi!
The following testcase takes very long time to compile, because
skip_simple_arithmetic decides to first call tree_invariant_p on
the second argument (and indirectly recurse there). I think before
canonicalization of operands for commutative binary expressions
(and for non-commutative ones always) it is pretty common that the
first operand is a constant, something which tree_invariant_p handles
immediately, so the following patch special cases that; I've added
there a tree_invariant_p call too after the checks, while it is not
really needed currently, tree_invariant_p has the same checks, I wanted
to be prepared in case tree_invariant_p changes. But if you think
I should avoid it, I can drop it too.
This is just a partial fix, I think one can certainly construct a testcase
which will still have horrible compile time complexity (but I've tried and
haven't managed to do so), so perhaps we should just limit the recursion
depth through skip_simple_arithmetic/tree_invariant_p with some defaulted
argument.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2025-03-11 Jakub Jelinek <ja...@redhat.com>
PR c/119183
* tree.cc (skip_simple_arithmetic): If first operand of binary
expr is TREE_CONSTANT or TREE_READONLY with no side-effects, call
tree_invariant_p on that operand first instead of on the second.
* gcc.dg/pr119183.c: New test.
--- gcc/tree.cc.jj 2025-03-08 00:07:01.848908327 +0100
+++ gcc/tree.cc 2025-03-10 17:04:48.630157371 +0100
@@ -4105,7 +4105,12 @@ skip_simple_arithmetic (tree expr)
expr = TREE_OPERAND (expr, 0);
else if (BINARY_CLASS_P (expr))
{
- if (tree_invariant_p (TREE_OPERAND (expr, 1)))
+ if ((TREE_CONSTANT (TREE_OPERAND (expr, 0))
+ || (TREE_READONLY (TREE_OPERAND (expr, 0))
+ && !TREE_SIDE_EFFECTS (TREE_OPERAND (expr, 0))))
+ && tree_invariant_p (TREE_OPERAND (expr, 0)))
+ expr = TREE_OPERAND (expr, 1);
+ else if (tree_invariant_p (TREE_OPERAND (expr, 1)))
expr = TREE_OPERAND (expr, 0);
else if (tree_invariant_p (TREE_OPERAND (expr, 0)))
expr = TREE_OPERAND (expr, 1);
--- gcc/testsuite/gcc.dg/pr119183.c.jj 2025-03-10 17:48:57.839774108 +0100
+++ gcc/testsuite/gcc.dg/pr119183.c 2025-03-10 17:48:22.960253026 +0100
@@ -0,0 +1,12 @@
+/* PR c/119183 */
+/* { dg-do compile } */
+
+int foo (void);
+#define A(x) (1.0f * (1.0f * (1.0f * (1.0f * (1.0f * (1.0f * (1.0f * (1.0f *
(x)))))))))
+
+float
+bar (float r)
+{
+ r += A (A (A (A (A (A (A (A (foo ()))))))));
+ return r;
+}
Jakub
