AVR: Fix PR120423 / PR116389.

The problem with PR120423 and PR116389 is that reload might assign an invalid
hard register to a paradoxical subreg.  For example with the test case from
the PR, it assigns (REG:QI 31) to the inner of (subreg:HI (QI) 0) which is
valid, but the subreg will be turned into (REG:HI 31) which is invalid
and triggers an ICE in postreload.

The problem only occurs with the old reload pass.

The patch maps the paradoxical subregs to a zero-extends which will be
allocated correctly.  For the 120423 testcases, the code is the same like
with -mlra (which doesn't implement the fix), so the patch doesn't even
introduce a performance penalty.

The patch is only needed for v15:  v14 is not affected, and in v16 reload
will be removed.

	PR rtl-optimization/120423
	PR rtl-optimization/116389
gcc/
	* config/avr/avr.md [-mno-lra]: Add pre-reload split to transform
	(left shift of) a paradoxical subreg to a (left shift of) zero-extend.
gcc/testsuite/
	* gcc.target/avr/torture/pr120423-1.c: New test.
	* gcc.target/avr/torture/pr120423-2.c: New test.
	* gcc.target/avr/torture/pr120423-116389.c: New test.

4 files changed, 116 insertions, 0 deletions

diff --git a/gcc/config/avr/avr.md b/gcc/config/avr/avr.md
index 01b8e4b..f8bbdc7 100644
--- a/gcc/config/avr/avr.md
+++ b/gcc/config/avr/avr.md
@@ -5273,6 +5273,41 @@
 ;;<< << << << << << << << << << << << << << << << << << << << << << << << << <<
 ;; arithmetic shift left
 
+;; Work around PR120423: Transform left shift of a paradoxical subreg
+;; into left shift of the zero-extended entity.
+(define_split ; PR120423
+  [(set (match_operand:HISI 0 "register_operand")
+        (ashift:HISI (subreg:HISI (match_operand:QIPSI 1 "nonimmediate_operand")
+                                  0)
+                     (match_operand:QI 2 "const_int_operand")))]
+  "!reload_completed
+   && !avropt_lra_p
+   && <HISI:SIZE> > <QIPSI:SIZE>"
+  [(set (match_dup 4)
+        (zero_extend:HISI (match_dup 5)))
+   (set (match_dup 0)
+        (ashift:HISI (match_dup 4)
+                     (match_dup 2)))]
+  {
+    operands[4] = gen_reg_rtx (<HISI:MODE>mode);
+    operands[5] = force_reg (<QIPSI:MODE>mode, operands[1]);
+  })
+
+;; Similar happens for PR116389.
+(define_split ; PR116389
+  [(set (match_operand:HISI 0 "register_operand")
+        (subreg:HISI (match_operand:QIPSI 1 "nonimmediate_operand")
+                     0))]
+  "!reload_completed
+   && !avropt_lra_p
+   && <HISI:SIZE> > <QIPSI:SIZE>"
+  [(set (match_dup 0)
+        (zero_extend:HISI (match_dup 2)))]
+  {
+    operands[2] = force_reg (<QIPSI:MODE>mode, operands[1]);
+  })
+
+
 ;; "ashlqi3"
 ;; "ashlqq3"  "ashluqq3"
 (define_expand "ashl<mode>3"
diff --git a/gcc/testsuite/gcc.target/avr/torture/pr120423-1.c b/gcc/testsuite/gcc.target/avr/torture/pr120423-1.c
new file mode 100644
index 0000000..91b4bbc
--- /dev/null
+++ b/gcc/testsuite/gcc.target/avr/torture/pr120423-1.c
@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+
+struct data
+{
+    int a;
+    int b;
+    long c;
+};
+
+unsigned char val;
+unsigned val2;
+
+void func1 (struct data *d)
+{
+    d->a = 0;
+    d->b = 0x100 * val - 1;
+}
+
+void func2 (struct data *d)
+{
+    d->a = 0;
+    d->c = 0x10000 * val2 - 1;
+}
+
+void func3 (struct data *d)
+{
+    d->a = 0;
+    d->c = 0x1000000 * val - 1;
+}
diff --git a/gcc/testsuite/gcc.target/avr/torture/pr120423-116389.c b/gcc/testsuite/gcc.target/avr/torture/pr120423-116389.c
new file mode 100644
index 0000000..928c135
--- /dev/null
+++ b/gcc/testsuite/gcc.target/avr/torture/pr120423-116389.c
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+
+struct T { int val; };
+
+void f_int (int);
+char* get_pos (void);
+struct T* get_pT (void);
+
+void func (char i)
+{
+    struct T t = * get_pT ();
+    unsigned diff = get_pos () - &i;
+
+    if (diff)
+    {
+        long val32 = t.val;
+        if (get_pos ())
+            val32 = diff;
+        if (get_pos ())
+            f_int (2 * val32);
+    }
+}
diff --git a/gcc/testsuite/gcc.target/avr/torture/pr120423-2.c b/gcc/testsuite/gcc.target/avr/torture/pr120423-2.c
new file mode 100644
index 0000000..56e6141
--- /dev/null
+++ b/gcc/testsuite/gcc.target/avr/torture/pr120423-2.c
@@ -0,0 +1,30 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-ffixed-18 -ffixed-20 -ffixed-22" } */
+
+struct data
+{
+    int a;
+    int b;
+    long c;
+};
+
+unsigned char val;
+unsigned val2;
+
+void func1 (struct data *d)
+{
+    d->a = 0;
+    d->b = 0x100 * val - 1;
+}
+
+void func2 (struct data *d)
+{
+    d->a = 0;
+    d->c = 0x10000 * val2 - 1;
+}
+
+void func3 (struct data *d)
+{
+    d->a = 0;
+    d->c = 0x1000000 * val - 1;
+}