From 2b4efc5db2aedb59196987300e14951d08cd7106 Mon Sep 17 00:00:00 2001
From: Jakub Jelinek <jakub@redhat.com>
Date: Thu, 15 Feb 2024 15:53:01 +0100
Subject: [PATCH] expand: Fix handling of asm goto outputs vs. PHI argument
adjustments [PR113921]
The Linux kernel and the following testcase distilled from it is
miscompiled, because tree-outof-ssa.cc (eliminate_phi) emits some
fixups on some of the edges (but doesn't commit edge insertions).
Later expand_asm_stmt emits further instructions on the same edge.
Now the problem is that expand_asm_stmt uses insert_insn_on_edge
to add its own fixups, but that function appends to the existing
sequence on the edge if any. And the bug triggers when the
fixup sequence emitted by eliminate_phi uses a pseudo which the
fixup sequence emitted by expand_asm_stmt later on sets.
So, we end up with
(set (reg A) (asm_operands ...))
and on one of the edges queued sequence
(set (reg C) (reg B)) // added by eliminate_phi
(set (reg B) (reg A)) // added by expand_asm_stmt
That is wrong, what we emit by expand_asm_stmt needs to be as close
to the asm_operands as possible (they aren't known until expand_asm_stmt
is called, the PHI fixup code assumes it is reg B which holds the right
value) and the PHI adjustments need to be done after it.
So, the following patch introduces a prepend_insn_to_edge function and
uses it from expand_asm_stmt, so that we queue
(set (reg B) (reg A)) // added by expand_asm_stmt
(set (reg C) (reg B)) // added by eliminate_phi
instead and so the value from the asm_operands output propagates correctly
to the PHI result.
2024-02-15 Jakub Jelinek <jakub@redhat.com>
PR middle-end/113921
* cfgrtl.h (prepend_insn_to_edge): New declaration.
* cfgrtl.cc (insert_insn_on_edge): Clarify behavior in function
comment.
(prepend_insn_to_edge): New function.
* cfgexpand.cc (expand_asm_stmt): Use prepend_insn_to_edge instead of
insert_insn_on_edge.
* gcc.target/i386/pr113921.c: New test.
---
gcc/cfgexpand.cc | 2 +-
gcc/cfgrtl.cc | 24 ++++++++++++++++++++++--
gcc/cfgrtl.h | 1 +
gcc/testsuite/gcc.target/i386/pr113921.c | 20 ++++++++++++++++++++
4 files changed, 44 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/i386/pr113921.c
diff --git a/gcc/cfgexpand.cc b/gcc/cfgexpand.cc
index d36dfc842e15..eef565eddb5d 100644
--- a/gcc/cfgexpand.cc
+++ b/gcc/cfgexpand.cc
@@ -3687,7 +3687,7 @@ expand_asm_stmt (gasm *stmt)
copy = get_insns ();
end_sequence ();
}
- insert_insn_on_edge (copy, e);
+ prepend_insn_to_edge (copy, e);
}
}
}
diff --git a/gcc/cfgrtl.cc b/gcc/cfgrtl.cc
index a8549d5f9864..15259c5e9847 100644
--- a/gcc/cfgrtl.cc
+++ b/gcc/cfgrtl.cc
@@ -25,7 +25,7 @@ along with GCC; see the file COPYING3. If not see
- CFG-aware instruction chain manipulation
delete_insn, delete_insn_chain
- Edge splitting and committing to edges
- insert_insn_on_edge, commit_edge_insertions
+ insert_insn_on_edge, prepend_insn_to_edge, commit_edge_insertions
- CFG updating after insn simplification
purge_dead_edges, purge_all_dead_edges
- CFG fixing after coarse manipulation
@@ -1966,7 +1966,8 @@ rtl_split_edge (edge edge_in)
/* Queue instructions for insertion on an edge between two basic blocks.
The new instructions and basic blocks (if any) will not appear in the
- CFG until commit_edge_insertions is called. */
+ CFG until commit_edge_insertions is called. If there are already
+ queued instructions on the edge, PATTERN is appended to them. */
void
insert_insn_on_edge (rtx pattern, edge e)
@@ -1986,6 +1987,25 @@ insert_insn_on_edge (rtx pattern, edge e)
end_sequence ();
}
+/* Like insert_insn_on_edge, but if there are already queued instructions
+ on the edge, PATTERN is prepended to them. */
+
+void
+prepend_insn_to_edge (rtx pattern, edge e)
+{
+ /* We cannot insert instructions on an abnormal critical edge.
+ It will be easier to find the culprit if we die now. */
+ gcc_assert (!((e->flags & EDGE_ABNORMAL) && EDGE_CRITICAL_P (e)));
+
+ start_sequence ();
+
+ emit_insn (pattern);
+ emit_insn (e->insns.r);
+
+ e->insns.r = get_insns ();
+ end_sequence ();
+}
+
/* Update the CFG for the instructions queued on edge E. */
void
diff --git a/gcc/cfgrtl.h b/gcc/cfgrtl.h
index e6062d4a469c..657cd08990bc 100644
--- a/gcc/cfgrtl.h
+++ b/gcc/cfgrtl.h
@@ -38,6 +38,7 @@ extern edge try_redirect_by_replacing_jump (edge, basic_block, bool);
extern void emit_barrier_after_bb (basic_block bb);
extern basic_block force_nonfallthru_and_redirect (edge, basic_block, rtx);
extern void insert_insn_on_edge (rtx, edge);
+extern void prepend_insn_to_edge (rtx, edge);
extern void commit_one_edge_insertion (edge e);
extern void commit_edge_insertions (void);
extern void print_rtl_with_bb (FILE *, const rtx_insn *, dump_flags_t);
diff --git a/gcc/testsuite/gcc.target/i386/pr113921.c b/gcc/testsuite/gcc.target/i386/pr113921.c
new file mode 100644
index 000000000000..f7efba741436
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr113921.c
@@ -0,0 +1,20 @@
+/* PR middle-end/113921 */
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+__attribute__((noipa)) long
+foo (void)
+{
+ long v;
+ asm volatile goto ("jmp %l2" : "=r" (v) : "0" (27) : : lab);
+ return v;
+lab:
+ return 42;
+}
+
+int
+main ()
+{
+ if (foo () != 42)
+ __builtin_abort ();
+}
--
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