[gcc r11-9154] [PR102627] Use at least natural mode during splitting hard reg live range

[gcc r11-9154] [PR102627] Use at least natural mode during splitting hard reg live range

[Vladimir Makarov]

https://gcc.gnu.org/g:99d21577f8a00196f3133fe1066de6e3e7d180c1

commit r11-9154-g99d21577f8a00196f3133fe1066de6e3e7d180c1
Author: Vladimir N. Makarov <vmakarov@redhat.com>
Date:   Fri Oct 8 10:16:09 2021 -0400

    [PR102627] Use at least natural mode during splitting hard reg live range
    
    In the PR test case SImode was used to split live range of cx on x86-64
    because it was the biggest mode for this hard reg in the function.  But
    all 64-bits of cx contain structure members.  We need always to use at least
    natural mode of hard reg in splitting to fix this problem.
    
    gcc/ChangeLog:
    
            PR rtl-optimization/102627
            * lra-constraints.c (split_reg): Use at least natural mode of hard reg.
    
    gcc/testsuite/ChangeLog:
    
            PR rtl-optimization/102627
            * gcc.target/i386/pr102627.c: New test.

Diff:
---
 gcc/lra-constraints.c                    |  5 ++--
 gcc/testsuite/gcc.target/i386/pr102627.c | 41 ++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/gcc/lra-constraints.c b/gcc/lra-constraints.c
index 5c2a2d7ce9c..aaacc4eabed 100644
--- a/gcc/lra-constraints.c
+++ b/gcc/lra-constraints.c
@@ -5805,11 +5805,12 @@ split_reg (bool before_p, int original_regno, rtx_insn *insn,
 	 part of a multi-word register.  In that case, just use the reg_rtx
 	 mode.  Do the same also if the biggest mode was larger than a register
 	 or we can not compare the modes.  Otherwise, limit the size to that of
-	 the biggest access in the function.  */
+	 the biggest access in the function or to the natural mode at least.  */
       if (mode == VOIDmode
 	  || !ordered_p (GET_MODE_PRECISION (mode),
 			 GET_MODE_PRECISION (reg_rtx_mode))
-	  || paradoxical_subreg_p (mode, reg_rtx_mode))
+	  || paradoxical_subreg_p (mode, reg_rtx_mode)
+	  || maybe_gt (GET_MODE_PRECISION (reg_rtx_mode), GET_MODE_PRECISION (mode)))
 	{
 	  original_reg = regno_reg_rtx[hard_regno];
 	  mode = reg_rtx_mode;
diff --git a/gcc/testsuite/gcc.target/i386/pr102627.c b/gcc/testsuite/gcc.target/i386/pr102627.c
new file mode 100644
index 00000000000..8ab9acaf002
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr102627.c
@@ -0,0 +1,41 @@
+/* PR rtl-optimization/102627 */
+/* { dg-do run } */
+/* { dg-options "-O1" } */
+
+int a, f, l, m, q, c, d, g;
+long b, e;
+struct g {
+  signed h;
+  signed i;
+  unsigned j;
+  unsigned k;
+};
+unsigned n;
+char o;
+int *p = &m;
+long r(int s) { return s && b ?: b; }
+long __attribute__((noipa)) v() {
+  l = 0 || r(n & o);
+  return q;
+}
+void w(int, unsigned, struct g x) {
+  c ?: a;
+  for (; d < 2; d++)
+    *p = x.k;
+}
+struct g __attribute__((noipa)) y() {
+  struct g h = {3, 908, 1, 20};
+  for (; g; g++)
+    ;
+  return h;
+}
+int main() {
+  long t;
+  struct g u = y();
+  t = e << f;
+  w(0, t, u);
+  v(0, 4, 4, 4);
+  if (m != 20)
+    __builtin_abort ();
+  return 0;
+}