diff mbox series

[v2,1/5] Improve must tail in RTL backend

Message ID 20240124193134.622934-2-ak@linux.intel.com
State New
Headers show
Series [v2,1/5] Improve must tail in RTL backend | expand

Commit Message

Andi Kleen Jan. 24, 2024, 7:30 p.m. UTC 
- Give error messages for all causes of non sibling call generation
- Don't override choices of other non sibling call checks with
must tail. This causes ICEs. The must tail attribute now only
overrides flag_optimize_sibling_calls locally.
- Error out when tree-tailcall failed to mark a must-tail call
sibcall. In this case it doesn't know the true reason and only gives
a vague message (this could be improved, but it's already useful without
that) tree-tailcall usually fails without optimization, so must
adjust the existing must-tail plugin test to specify -O2.
---
 gcc/calls.cc                                  | 31 +++++++++++++------
 .../gcc.dg/plugin/must-tail-call-1.c          |  1 +
 2 files changed, 22 insertions(+), 10 deletions(-)
diff mbox series

Patch

diff --git a/gcc/calls.cc b/gcc/calls.cc
index 01f447347437..3115807b7788 100644
--- a/gcc/calls.cc
+++ b/gcc/calls.cc
@@ -2650,7 +2650,9 @@  expand_call (tree exp, rtx target, int ignore)
   /* The type of the function being called.  */
   tree fntype;
   bool try_tail_call = CALL_EXPR_TAILCALL (exp);
-  bool must_tail_call = CALL_EXPR_MUST_TAIL_CALL (exp);
+  /* tree-tailcall decided not to do tail calls. Error for the musttail case.  */
+  if (!try_tail_call)
+      maybe_complain_about_tail_call (exp, "cannot tail-call: other reasons");
   int pass;
 
   /* Register in which non-BLKmode value will be returned,
@@ -3021,10 +3023,22 @@  expand_call (tree exp, rtx target, int ignore)
      pushed these optimizations into -O2.  Don't try if we're already
      expanding a call, as that means we're an argument.  Don't try if
      there's cleanups, as we know there's code to follow the call.  */
-  if (currently_expanding_call++ != 0
-      || (!flag_optimize_sibling_calls && !CALL_FROM_THUNK_P (exp))
-      || args_size.var
-      || dbg_cnt (tail_call) == false)
+  if (currently_expanding_call++ != 0)
+    {
+      maybe_complain_about_tail_call (exp, "cannot tail-call: inside another call");
+      try_tail_call = 0;
+    }
+  if (!flag_optimize_sibling_calls
+	&& !CALL_FROM_THUNK_P (exp)
+	&& !CALL_EXPR_MUST_TAIL_CALL (exp))
+    try_tail_call = 0;
+  if (args_size.var)
+    {
+      /* ??? correct message?  */
+      maybe_complain_about_tail_call (exp, "cannot tail-call: stack space needed");
+      try_tail_call = 0;
+    }
+  if (dbg_cnt (tail_call) == false)
     try_tail_call = 0;
 
   /* Workaround buggy C/C++ wrappers around Fortran routines with
@@ -3045,15 +3059,12 @@  expand_call (tree exp, rtx target, int ignore)
 	    if (MEM_P (*iter))
 	      {
 		try_tail_call = 0;
+		maybe_complain_about_tail_call (exp,
+				"cannot tail-call: hidden string length argument");
 		break;
 	      }
 	}
 
-  /* If the user has marked the function as requiring tail-call
-     optimization, attempt it.  */
-  if (must_tail_call)
-    try_tail_call = 1;
-
   /*  Rest of purposes for tail call optimizations to fail.  */
   if (try_tail_call)
     try_tail_call = can_implement_as_sibling_call_p (exp,
diff --git a/gcc/testsuite/gcc.dg/plugin/must-tail-call-1.c b/gcc/testsuite/gcc.dg/plugin/must-tail-call-1.c
index 3a6d4cceaba7..44af361e2925 100644
--- a/gcc/testsuite/gcc.dg/plugin/must-tail-call-1.c
+++ b/gcc/testsuite/gcc.dg/plugin/must-tail-call-1.c
@@ -1,4 +1,5 @@ 
 /* { dg-do compile { target tail_call } } */
+/* { dg-options "-O2" } */
 /* { dg-options "-fdelayed-branch" { target sparc*-*-* } } */
 
 extern void abort (void);