[to-be-committed][RISC-V] Restore inline expansion of block moves on RISC-V in some cases

[Jeffrey Law]

Edwin's patch to add a --param for a size threshold on block moves 
inadvertently disabled using inline block moves for cases where the 
count is unknown.  This caused testsuite regressions (I don't remember 
which test, it was ~6 weeks ago if not longer).  I'd hoped Edwin would 
see the new failures, but I suspect he's buried by transition stuff with 
Rivos/Meta.

This patch restores prior behavior when the count is unknown and no 
--param was specified.

Bootstrapped and regression tested on both the BPI and Pioneer systems 
and regression tested on riscv{32,64}-elf as well.

Pushing to the trunk after pre-commit CI does its thing.

Jeffdiff --git a/gcc/config/riscv/riscv-string.cc b/gcc/config/riscv/riscv-string.cc
index c5710e4c8962..d888dac8e5f7 100644
--- a/gcc/config/riscv/riscv-string.cc
+++ b/gcc/config/riscv/riscv-string.cc
@@ -1249,7 +1249,7 @@ expand_block_move (rtx dst_in, rtx src_in, rtx length_in, 
bool movmem_p)
               && length > riscv_memcpy_size_threshold)
        return false;
     }
-  else
+  else if (riscv_memmove_size_threshold != -1)
     return false;
 
   /* Inlining general memmove is a pessimisation: we can't avoid having to
@@ -1641,7 +1641,7 @@ expand_vec_setmem (rtx dst_in, rtx length_in, rtx 
fill_value_in)
          && length > riscv_memset_size_threshold)
        return false;
     }
-  else
+  else if (riscv_memset_size_threshold != -1)
     return false;
 
   rtx dst_addr = copy_addr_to_reg (XEXP (dst_in, 0));