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.

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 7e819f37446c8320b7d4def4927e32b663a00b1c..4cfcc420fea5090b8e2719d094b6e1c620ba4cf5 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;