https://gcc.gnu.org/g:2edb50a310896da72710dba7724a3b4a541a1cbb
commit r16-1065-g2edb50a310896da72710dba7724a3b4a541a1cbb
Author: Alexandre Oliva <ol...@adacore.com>
Date: Mon Jun 2 20:21:45 2025 -0300
[lra] force reg update after spilling to memory [PR120424]
In the added C++ testcase, a stack slot at a negative sp offset is
used to hold a value across a call.
There are a couple of causes that directly lead to this outcome:
- the -fstack-clash-protection and -fnon-call-exception options, that
cause arm_frame_pointer_required to flip from false to true when the
first pseudo gets spilled to memory;
- when the affected pseudo is spilled to memory, we fail to update lra
regno info, because the insns that reference it are already on the
lra_constraint_insn_stack;
There is another potentially-related issue:
- when we notice that the frame pointer can no longer be eliminated to
the stack pointer, we immediately clear can_eliminate, and also
prev_can_eliminate, but update_reg_eliminate relied on the latter to
tell that it needs to propagate a previous_offset to the
newly-selected elimination, or restore the original offsets.
This patch ensures that we update insn register info after spilling a
pseudo to memory, and enables update_reg_eliminate to recognize the
case in which a previously-preferred elimination is disabled
regardless of prev_can_eliminate.
for gcc/ChangeLog
PR rtl-optimization/120424
PR middle-end/118939
* lra-spills.cc (spill_pseudos): Update insn regno info.
* lra-eliminations.cc (update_reg_eliminate): Recognize
disabling of active elimination regardless of
prev_can_eliminate.
for gcc/testsuite/ChangeLog
PR rtl-optimization/120424
PR middle-end/118939
* g++.target/arm/pr120424.C: New.
* gnat.dg/controlled9.adb: New.
* gnat.dg/controlled9_pkg.ads: New.
Diff:
---
gcc/lra-eliminations.cc | 2 +-
gcc/lra-spills.cc | 2 +-
gcc/testsuite/g++.target/arm/pr120424.C | 34 +++++++++++++++++++++++++++++++
gcc/testsuite/gnat.dg/controlled9.adb | 10 +++++++++
gcc/testsuite/gnat.dg/controlled9_pkg.ads | 5 +++++
5 files changed, 51 insertions(+), 2 deletions(-)
diff --git a/gcc/lra-eliminations.cc b/gcc/lra-eliminations.cc
index d84a7d1ee99f..bb708b007a4e 100644
--- a/gcc/lra-eliminations.cc
+++ b/gcc/lra-eliminations.cc
@@ -1185,7 +1185,7 @@ update_reg_eliminate (bitmap insns_with_changed_offsets)
setup_can_eliminate (ep, false);
continue;
}
- if (ep->can_eliminate != prev && elimination_map[ep->from] == ep)
+ if (!ep->can_eliminate && elimination_map[ep->from] == ep)
{
/* We cannot use this elimination anymore -- find another
one. */
diff --git a/gcc/lra-spills.cc b/gcc/lra-spills.cc
index fc912c43ce6e..4febc693d283 100644
--- a/gcc/lra-spills.cc
+++ b/gcc/lra-spills.cc
@@ -556,7 +556,7 @@ spill_pseudos (void)
fprintf (lra_dump_file,
"Changing spilled pseudos to memory in insn #%u\n",
INSN_UID (insn));
- lra_push_insn (insn);
+ lra_push_insn_and_update_insn_regno_info (insn);
if (lra_reg_spill_p || targetm.different_addr_displacement_p ())
lra_set_used_insn_alternative (insn, LRA_UNKNOWN_ALT);
}
diff --git a/gcc/testsuite/g++.target/arm/pr120424.C
b/gcc/testsuite/g++.target/arm/pr120424.C
new file mode 100644
index 000000000000..4d0e49013c04
--- /dev/null
+++ b/gcc/testsuite/g++.target/arm/pr120424.C
@@ -0,0 +1,34 @@
+/* { dg-do compile } */
+/* { dg-options "-march=armv7 -O2 -fstack-clash-protection
-fnon-call-exceptions" } */
+/* { dg-final { scan-assembler-not {#-8} } } */
+/* LRA register elimination gets confused when register spilling
+ causes arm_frame_pointer_required to switch from false to true, and
+ ends up using a stack slot below sp. */
+
+void f() {
+ int i = 0, j = 0;
+ asm ("" : : "m" (i), "m" (j));
+}
+
+void g(void (*fn[])(), int i)
+{
+ auto fn0 = fn[i+0];
+ auto fn1 = fn[i+1];
+ auto fn2 = fn[i+2];
+ auto fn3 = fn[i+3];
+ fn0();
+ fn1();
+ if (!fn2)
+ throw i+2;
+ fn2();
+ fn3();
+ fn0();
+ fn1();
+}
+
+int
+main()
+{
+ void (*fn[4])() = { f, f, f, f };
+ g (fn, 0);
+}
diff --git a/gcc/testsuite/gnat.dg/controlled9.adb
b/gcc/testsuite/gnat.dg/controlled9.adb
new file mode 100644
index 000000000000..fb7acce854e1
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/controlled9.adb
@@ -0,0 +1,10 @@
+-- { dg-do run }
+-- { dg-options "-O1 -fstack-check" }
+-- from PR middle-end/118939
+
+with Controlled9_Pkg;
+procedure Controlled9 is
+ S : constant Controlled9_Pkg.T_Access := new Controlled9_Pkg.T;
+begin
+ null;
+end Controlled9;
diff --git a/gcc/testsuite/gnat.dg/controlled9_pkg.ads
b/gcc/testsuite/gnat.dg/controlled9_pkg.ads
new file mode 100644
index 000000000000..d0e7c28273e9
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/controlled9_pkg.ads
@@ -0,0 +1,5 @@
+with Ada.Finalization;
+package Controlled9_Pkg is
+ type T is new Ada.Finalization.Controlled with null record;
+ type T_Access is access all T;
+end Controlled9_Pkg;
