[gcc r10-9832] rtl-optimization/80960 - avoid creating garbage RTL in DSE

[gcc r10-9832] rtl-optimization/80960 - avoid creating garbage RTL in DSE

[Richard Biener]

https://gcc.gnu.org/g:47d3815f0669800666f1dd69f0c5cfecc617a12b

commit r10-9832-g47d3815f0669800666f1dd69f0c5cfecc617a12b
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Jan 27 15:35:52 2021 +0100

    rtl-optimization/80960 - avoid creating garbage RTL in DSE
    
    The following avoids repeatedly turning VALUE RTXen into
    sth useful and re-applying a constant offset through get_addr
    via DSE check_mem_read_rtx.  Instead perform this once for
    all stores to be visited in check_mem_read_rtx.  This avoids
    allocating 1.6GB of garbage PLUS RTXen on the PR80960
    testcase, fixing the memory usage regression from old GCC.
    
    2021-01-27  Richard Biener  <rguenther@suse.de>
    
            PR rtl-optimization/80960
            * dse.c (check_mem_read_rtx): Call get_addr on the
            offsetted address.
    
    (cherry picked from commit a523add327c6cfdd68cf9b788ea808068d0f508c)

Diff:
---
 gcc/dse.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/gcc/dse.c b/gcc/dse.c
index 68ab4383d50..ec6f7b63449 100644
--- a/gcc/dse.c
+++ b/gcc/dse.c
@@ -2199,6 +2199,11 @@ check_mem_read_rtx (rtx *loc, bb_info_t bb_info)
     }
   if (maybe_ne (offset, 0))
     mem_addr = plus_constant (get_address_mode (mem), mem_addr, offset);
+  /* Avoid passing VALUE RTXen as mem_addr to canon_true_dependence
+     which will over and over re-create proper RTL and re-apply the
+     offset above.  See PR80960 where we almost allocate 1.6GB of PLUS
+     RTXen that way.  */
+  mem_addr = get_addr (mem_addr);
 
   if (group_id >= 0)
     {