From: Alexandre Oliva <oliva@gnu.org>
Date: Fri, 11 Jul 2025 01:21:31 +0000 (-0300)
Subject: arm: prevent impossible tail- long-calls with static chain [PR119430]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f5166f5badb190eec5d3707fe25ad33febf1969e;p=thirdparty%2Fgcc.git

arm: prevent impossible tail- long-calls with static chain [PR119430]

When a function call uses up all argument registers, and needs IP for
the static chain, there aren't any call-clobbered registers left for
reload to assign as the sibcall target, when -mlong-calls is enabled.
Use the same logic that does the job for indirect calls to prevent
tail calls in this case.

With this change, it is possible to bootstrap armv7a-linux-gnu with
both -O3 and lto, but only with both -mlong-calls and
-ffunction-sections.

Without -mlong-calls, linker veneer thunks may clobber the static
chain register set up by callers in one lto unit, preventing them from
reaching the callee in a separate lto unit.  -ffunction-sections is
required for -mlong-calls to be effective, because both caller and
callee are in the same section, and that disables long-calls when
!flag_reorder_blocks_and_partition.

gcc/ChangeLog

	PR target/119430
	* config/arm/arm.cc (arm_function_ok_for_sibcall): Disable
	sibcalls for long-calls that use all call-clobbered
	general-purpose registers, including the static chain.
---

diff --git a/gcc/config/arm/arm.cc b/gcc/config/arm/arm.cc
index ec21fb96b66..0a1f6612d07 100644
--- a/gcc/config/arm/arm.cc
+++ b/gcc/config/arm/arm.cc
@@ -7983,10 +7983,14 @@ arm_function_ok_for_sibcall (tree decl, tree exp)
      address.  But we only have r0-r3 and ip in that class.  If r0-r3 all hold
      function arguments, then we can only use IP.  But IP may be needed in the
      epilogue (for PAC validation), or for passing the static chain.  We have
-     to disable the tail call if nothing is available.  */
-  if (!decl
-      && ((CALL_EXPR_BY_DESCRIPTOR (exp) && !flag_trampolines)
-	  || arm_current_function_pac_enabled_p()))
+     to disable the tail call if nothing is available.  Long-calls are
+     effectively handled as indirect calls, so handle that as well.  */
+  if ((!decl
+       && ((CALL_EXPR_BY_DESCRIPTOR (exp) && !flag_trampolines)
+	   || arm_current_function_pac_enabled_p ()))
+      || (decl && arm_is_long_call_p (decl)
+	  && (CALL_EXPR_STATIC_CHAIN (exp)
+	      || arm_current_function_pac_enabled_p ())))
     {
       tree fntype = TREE_TYPE (TREE_TYPE (CALL_EXPR_FN (exp)));
       CUMULATIVE_ARGS cum;