The mn103 adddi3_degenerate pattern looks something like this:
(define_insn_and_split "*adddi3_degenerate"
[(set (match_operand:SI 0 "register_operand" "=&r,&r")
(match_operand:SI 2 "nonmemory_operand" " 0, 0"))
(set (match_operand:SI 1 "register_operand" "=r , r")
(plus:SI (match_operand:SI 3 "register_operand" "%1 , r")
(match_operand:SI 4 "nonmemory_operand" "ri, r")))
(clobber (reg:CC CC_REG))]
[ ... ]
It has gcc_assert (!reg_overlap_mentioned_p (operands[0], operands[1]))
out of an abundance of caution I suppose.
The problem is we can be called with
operands[0]: (subreg:SI (reg:DI X) 0))
operands[1]: (subreg:SI (reg:DI X) 4))
reg_overlap_mentioned_p has this comment:
> /* Nonzero if modifying X will affect IN. If X is a register or a SUBREG,
> we check if any register number in X conflicts with the relevant register
> numbers.
Of course in this case the writes will not stomp on each other and are
safe. I wandered around rtlanal.c but never found anything which would
match the test we really want here. I could just weaken the assert for
subregs, possibly using read_modify_subreg_p, but it just doesn't seem
worth the effort to save this assert.
Removing the assert fixes a few dozen testsuite failures and does not
introduce any regressions on the mn103 target.
Installing on the trunk.
Jeff
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 949061a369e..4fc01e9f9dd 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2018-11-16 Jeff Law <l...@redhat.com>
+
+ * config/mn10300/mn10300.md (adddi3_degenerate): Remove bogus
+ gcc_assert.
+
2018-11-16 Sandra Loosemore <san...@codesourcery.com>
PR middle-end/23197
diff --git a/gcc/config/mn10300/mn10300.md b/gcc/config/mn10300/mn10300.md
index 9350a502c68..c01d3d085df 100644
--- a/gcc/config/mn10300/mn10300.md
+++ b/gcc/config/mn10300/mn10300.md
@@ -753,7 +753,6 @@
rtx scratch = NULL_RTX;
if (!rtx_equal_p (operands[0], operands[2]))
{
- gcc_assert (!reg_overlap_mentioned_p (operands[0], operands[1]));
if (reg_overlap_mentioned_p (operands[0], operands[3])
|| reg_overlap_mentioned_p (operands[0], operands[4]))
{
