From: Tamar Christina <tamar.christina@arm.com>
Date: Fri, 12 Jun 2026 10:55:46 +0000 (+0100)
Subject: middle-end: introduce IFN_VARYING for temporary statements [PR125597]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ad36cd942cd9c16df93ada46af38e72cf4e15981;p=thirdparty%2Fgcc.git

middle-end: introduce IFN_VARYING for temporary statements [PR125597]

This defines a new IFN "VARYING" to indicate that the operation has no current
defining statement and so things like range analysis should just not report
anything yet.

In the vectorizer we can create new SSA variables that are only defined after
vectorization is finishing.  For instance the actual control statement for
masked loops.

However intermediate values need to be able to perform build expressions using
this SSA name but since GCC 16 ranger now tries to analyze these and we ICE.

This replaces the uses of gimple_nop in the definition with a value with a more
defined semantics.

gcc/ChangeLog:

	PR tree-optimization/125597
	* internal-fn.def (VARYING): New.
	* doc/ifn.texi: Document it.
	* internal-fn.cc (expand_VARYING): New.
	* internal-fn.h (expand_VARYING): New.
	* tree-cfg.cc (verify_gimple_call): Check for leaked IFN_VARYING.
---

diff --git a/gcc/doc/ifn.texi b/gcc/doc/ifn.texi
index 95813a26473..9a2c60a5768 100644
--- a/gcc/doc/ifn.texi
+++ b/gcc/doc/ifn.texi
@@ -1546,5 +1546,11 @@ The @code{IFN_FLOATTOBITINT} internal function is expanded by the
 The @code{IFN_BITINTTOFLOAT} internal function is expanded by the
 @code{expand_BITINTTOFLOAT} function.
 
+@cindex @code{IFN_VARYING} internal function
+@item @samp{IFN_VARYING}
+Use @code{IFN_VARYING} as a temporary placeholder for a value whose
+definition is still being built by the current pass.  The pass that creates
+it must replace it before finishing; the verifier rejects any remaining calls.
+
 @end table
 
diff --git a/gcc/internal-fn.cc b/gcc/internal-fn.cc
index 8a4622da794..0138c6f7ef0 100644
--- a/gcc/internal-fn.cc
+++ b/gcc/internal-fn.cc
@@ -5686,6 +5686,13 @@ expand_MASK_CALL (internal_fn, gcall *)
   gcc_unreachable ();
 }
 
+void
+expand_VARYING (internal_fn, gcall *)
+{
+  /* This IFN should reach expand.  */
+  gcc_unreachable ();
+}
+
 void
 expand_MULBITINT (internal_fn, gcall *stmt)
 {
diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
index a9fb933021f..af9f92950c7 100644
--- a/gcc/internal-fn.def
+++ b/gcc/internal-fn.def
@@ -622,6 +622,10 @@ DEF_INTERNAL_FN (CO_FRAME, ECF_PURE | ECF_NOTHROW | ECF_LEAF, NULL)
 /* A NOP function with arbitrary arguments and return value.  */
 DEF_INTERNAL_FN (NOP, ECF_CONST | ECF_LEAF | ECF_NOTHROW, NULL)
 
+/* A GIMPLE value with no definition and not Virtual Opeands for temporary
+   assignment cases within a pass.  */
+DEF_INTERNAL_FN (VARYING , ECF_NOVOPS | ECF_LEAF | ECF_NOTHROW, NULL)
+
 /* Temporary vehicle for __builtin_shufflevector.  */
 DEF_INTERNAL_FN (SHUFFLEVECTOR, ECF_CONST | ECF_LEAF | ECF_NOTHROW, NULL)
 
diff --git a/gcc/internal-fn.h b/gcc/internal-fn.h
index bd9ba8d6929..30930f388b0 100644
--- a/gcc/internal-fn.h
+++ b/gcc/internal-fn.h
@@ -275,6 +275,7 @@ extern void expand_SPACESHIP (internal_fn, gcall *);
 extern void expand_TRAP (internal_fn, gcall *);
 extern void expand_ASSUME (internal_fn, gcall *);
 extern void expand_MASK_CALL (internal_fn, gcall *);
+extern void expand_VARYING (internal_fn, gcall *);
 extern void expand_MULBITINT (internal_fn, gcall *);
 extern void expand_DIVMODBITINT (internal_fn, gcall *);
 extern void expand_FLOATTOBITINT (internal_fn, gcall *);
diff --git a/gcc/tree-cfg.cc b/gcc/tree-cfg.cc
index 8fb80b8121e..dc07dde8cfd 100644
--- a/gcc/tree-cfg.cc
+++ b/gcc/tree-cfg.cc
@@ -3419,6 +3419,14 @@ verify_gimple_call (gcall *stmt)
 	  }
     }
 
+  /* IFN_VARING is not allowed to be present after the completion of any pass
+     as it should have been replaced.  */
+  if (gimple_call_internal_p (stmt, IFN_VARYING))
+    {
+      error ("%<.VARYING%> calls should have been replaced and are not allowed "
+	     "outside of the pass that introduced them");
+      return true;
+    }
   /* ???  The C frontend passes unpromoted arguments in case it
      didn't see a function declaration before the call.  So for now
      leave the call arguments mostly unverified.  Once we gimplify