[committed] testsuite: Add testcase for already fixed PR [PR126576]

Hi!

This testcase got fixed with r17-2843, but the testcase is sufficiently
different from the other one that it is worth having both.

Tested on x86_64-linux and i686-linux, committed to trunk as obvious.

2026-08-03  Jakub Jelinek  <[email protected]>

	PR tree-optimization/126576
	* gcc.dg/torture/pr126576.c: New test.

--- gcc/testsuite/gcc.dg/torture/pr126576.c.jj	2026-08-03 11:45:31.427027382 +0200
+++ gcc/testsuite/gcc.dg/torture/pr126576.c	2026-08-03 11:46:29.331288867 +0200
@@ -0,0 +1,43 @@
+/* PR tree-optimization/126576 */
+/* { dg-do run } */
+
+#if __DBL_MANT_DIG__ == 53 && __DBL_MAX_10_EXP__ == 308 \
+    && __DBL_HAS_INFINITY__ && __FLT_EVAL_METHOD__ == 0
+int v;
+
+[[gnu::noipa]] void
+bar (int x)
+{
+  v |= x;
+}
+
+[[gnu::noipa]] double
+foo (double x)
+{
+  double a = x * x;
+  if (__builtin_isinf (a) && !__builtin_isinf (x))
+    bar (1);
+  double b = a * 3.0;
+  if (__builtin_isinf (b) && !__builtin_isinf (a))
+    bar (2);
+  return b;
+}
+#endif
+
+int
+main ()
+{
+#if __DBL_MANT_DIG__ == 53 && __DBL_MAX_10_EXP__ == 308 \
+    && __DBL_HAS_INFINITY__ && __FLT_EVAL_METHOD__ == 0
+  foo (1e154);
+  if (v != 2)
+    __builtin_abort ();
+  v = 0;
+  foo (1e152);
+  if (v != 0)
+    __builtin_abort ();
+  foo (1e155);
+  if (v != 1)
+    __builtin_abort ();
+#endif    
+}

	Jakub