[gcc r14-6781] aarch64: Fix early RA handling of deleted insns [PR113094]

[Richard Sandiford]

https://gcc.gnu.org/g:803d222e533efbc385411d4b5a2d0ec0551b9f16

commit r14-6781-g803d222e533efbc385411d4b5a2d0ec0551b9f16
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Thu Dec 21 10:20:19 2023 +0000

    aarch64: Fix early RA handling of deleted insns [PR113094]
    
    The testcase constructs a sequence of insns that are fully dead
    and yet (due to forced options) are not removed as such.  This
    triggered a case where we would emit a meaningless reload for a
    to-be-deleted insn.
    
    We can't delete the insns first because that might disrupt the
    iteration ranges.  So this patch turns them into notes before
    the walk and then continues to delete them properly afterwards.
    
    gcc/
            PR target/113094
            * config/aarch64/aarch64-early-ra.cc (apply_allocation): Stub
            out instructions that are going to be deleted before iterating
            over the rest.
    
    gcc/testsuite/
            PR target/113094
            * gcc.target/aarch64/pr113094.c: New test.

Diff:
---
 gcc/config/aarch64/aarch64-early-ra.cc      |  3 +++
 gcc/testsuite/gcc.target/aarch64/pr113094.c | 10 ++++++++++
 2 files changed, 13 insertions(+)

diff --git a/gcc/config/aarch64/aarch64-early-ra.cc b/gcc/config/aarch64/aarch64-early-ra.cc
index 24415bd829c..5d2da3e1110 100644
--- a/gcc/config/aarch64/aarch64-early-ra.cc
+++ b/gcc/config/aarch64/aarch64-early-ra.cc
@@ -3210,6 +3210,9 @@ early_ra::maybe_convert_to_strided_access (rtx_insn *insn)
 void
 early_ra::apply_allocation ()
 {
+  for (auto *insn : m_dead_insns)
+    set_insn_deleted (insn);
+
   rtx_insn *prev;
   for (auto insn_range : m_insn_ranges)
     for (rtx_insn *insn = insn_range.first;
diff --git a/gcc/testsuite/gcc.target/aarch64/pr113094.c b/gcc/testsuite/gcc.target/aarch64/pr113094.c
new file mode 100644
index 00000000000..b79e1f744ed
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/pr113094.c
@@ -0,0 +1,10 @@
+/* { dg-options "-fno-tree-dse -Ofast -fno-tree-coalesce-vars -fno-dce -fno-tree-dce" } */
+
+struct TV4 {
+  __attribute__((vector_size(sizeof(int) * 4))) int v;
+};
+void modify() {
+  struct TV4 __trans_tmp_1, temp;
+  temp.v[0] = temp.v[3] = 0;
+  __trans_tmp_1 = temp;
+}