[gcc r14-3188] MMIX: Handle LRA FP-to-SP-elimination oddity

[Hans-Peter Nilsson]

https://gcc.gnu.org/g:9568ff597e8190b219564b912a4f608c9b95cf13

commit r14-3188-g9568ff597e8190b219564b912a4f608c9b95cf13
Author: Hans-Peter Nilsson <hp@axis.com>
Date:   Sun Aug 13 03:14:11 2023 +0200

    MMIX: Handle LRA FP-to-SP-elimination oddity
    
    When LRA is in progress, it can try and validate insns
    half-way through frame-pointer (FP) to stack-pointer (SP)
    elimination.  Operands have then been substituted where the
    offset is from the SP elimination but the register is the
    (hard) frame-pointer:
    
    lra-eliminations.cc:lra_eliminate_regs_1:370:
     rtx to = subst_p ? ep->to_rtx : ep->from_rtx;
    
    In this regard reload played nicely.  Unfortunately, the
    frame_pointer_operand predicate in mmix/predicates.md barfs
    on such an address.  This broke the use of the MMIX
    frame_pointer_operand predicate (and the Yf constraint),
    used only in the nonlocal_goto_receiver expansion (which is
    used in e.g. code generated for C++ "catch").
    
    Force MMIX frame_pointer_operand to accept an FP+offset for
    the duration of lra_in_progress.
    
            * config/mmix/predicates.md (frame_pointer_operand): Handle FP+offset
            when lra_in_progress.

Diff:
---
 gcc/config/mmix/predicates.md | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/gcc/config/mmix/predicates.md b/gcc/config/mmix/predicates.md
index 4a9b0177a786..64e77fa92d00 100644
--- a/gcc/config/mmix/predicates.md
+++ b/gcc/config/mmix/predicates.md
@@ -171,4 +171,14 @@
     (match_code "plus")
     (match_code "reg" "0")
     (match_code "const_int" "1")
-    (match_test "XEXP (op, 0) == stack_pointer_rtx"))))
+    (ior
+     (match_test "XEXP (op, 0) == stack_pointer_rtx")
+     ;; We can temporarily have a FP+offset here, where we (for FP)
+     ;; accept only FP and the equivalent elimination of SP+offset.
+     ;; See lra_eliminate_regs_1 in lra-eliminations.cc c:a line 370:
+     ;;  "rtx to = subst_p ? ep->to_rtx : ep->from_rtx;"
+     (and
+      (match_test "lra_in_progress")
+      (ior
+       (match_test "XEXP (op, 0) == hard_frame_pointer_rtx")
+       (match_test "XEXP (op, 0) == frame_pointer_rtx")))))))