recip: Reset range info when replacing sqrt with rsqrt [PR120638]

This pass reuses a SSA_NAME on the lhs of sqrt etc. call as lhs
of .RSQRT etc. call.  The following testcase is miscompiled since my recent
ranger cast changes, because we compute (correct) range for sqrtf argument
as well as result but then recip pass keeps using that range for the .RQSRT
call which returns 1. / sqrt, so the function then returns 0.5f
unconditionally.
Note, on foo this is a regression from GCC 15, but on bar it regressed
already with the r14-536 change.

2025-06-12  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/120638
	* tree-ssa-math-opts.cc (pass_cse_reciprocals::execute): Call
	reset_flow_sensitive_info on arg1.

	* gcc.dg/pr120638.c: New test.

(cherry picked from commit 8804e5b5b127b27d099d0c361fa2161d0b13edef)

diff --git a/gcc/testsuite/gcc.dg/pr120638.c b/gcc/testsuite/gcc.dg/pr120638.c
new file mode 100644 (file)
index 0000000..4a057a0
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr120638.c
@@ -0,0 +1,31 @@
+/* PR tree-optimization/120638 */
+/* { dg-do run } */
+/* { dg-options "-O2 -ffast-math" } */
+
+extern float sqrtf (float x);
+
+__attribute__((noipa)) float
+foo (unsigned int s)
+{
+  return 0.5f / sqrtf (1.f + s);
+}
+
+__attribute__((noipa)) float
+bar (float s)
+{
+  if (s < 0.0 || s > 65535.0f)
+    __builtin_unreachable ();
+  return 0.5f / sqrtf (1.f + s);
+}
+
+int
+main ()
+{
+  if (__builtin_fabsf (foo (3) - 0.25f) > 0.00390625f
+      || __builtin_fabsf (foo (15) - 0.125f) > 0.00390625f
+      || __builtin_fabsf (foo (63) - 0.0625f) > 0.00390625f
+      || __builtin_fabsf (bar (3.0f) - 0.25f) > 0.00390625f
+      || __builtin_fabsf (bar (15.0f) - 0.125f) > 0.00390625f
+      || __builtin_fabsf (bar (63.0f) - 0.0625f) > 0.00390625f)
+    __builtin_abort ();
+}

diff --git a/gcc/tree-ssa-math-opts.cc b/gcc/tree-ssa-math-opts.cc
index eb03ebe102ad14a8ccf2df4aea684495a279dbec..1954c287c0ac8a016f367d11020cd8a80fabc42c 100644 (file)
--- a/gcc/tree-ssa-math-opts.cc
+++ b/gcc/tree-ssa-math-opts.cc
@@ -1053,6 +1053,7 @@ pass_cse_reciprocals::execute (function *fun)
                    continue;
 
                  gimple_replace_ssa_lhs (call, arg1);
+                 reset_flow_sensitive_info (arg1);
                  if (gimple_call_internal_p (call) != (ifn != IFN_LAST))
                    {
                      auto_vec<tree, 4> args;