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 60cc0c2a3eb2587f5c339a20baf7503dab962585..92ea322de03d77bb4f8ec766d29e95465e3e3d61 100644 (file)
--- a/gcc/tree-ssa-math-opts.cc
+++ b/gcc/tree-ssa-math-opts.cc
@@ -1052,6 +1052,7 @@ 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;