[gcc r12-7786] target/102125 - alternative memcpy folding improvement

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:d9792f8d227cdd409c2b082ef0685b47ccfaa334

commit r12-7786-gd9792f8d227cdd409c2b082ef0685b47ccfaa334
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Mar 23 14:53:49 2022 +0100

    target/102125 - alternative memcpy folding improvement
    
    The following extends the heuristical memcpy folding path with the
    ability to use misaligned accesses on strict-alignment targets just
    like the size-based path does.  That avoids regressing the following
    testcase on arm
    
        uint64_t bar64(const uint8_t *rData1)
        {
            uint64_t buffer;
            memcpy(&buffer, rData1, sizeof(buffer));
            return buffer;
        }
    
    when r12-3482-g5f6a6c91d7c592 is reverted.
    
    2022-03-23  Richard Biener  <rguenther@suse.de>
    
            PR target/102125
            * gimple-fold.cc (gimple_fold_builtin_memory_op): Allow the
            use of movmisalign when either the source or destination
            decl is properly aligned.

Diff:
---
 gcc/gimple-fold.cc | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
index c9179abb27e..5eff7d68ac1 100644
--- a/gcc/gimple-fold.cc
+++ b/gcc/gimple-fold.cc
@@ -1254,7 +1254,11 @@ gimple_fold_builtin_memory_op (gimple_stmt_iterator *gsi,
 	    srcvar = fold_build2 (MEM_REF, desttype, src, off0);
 	  else
 	    {
-	      if (STRICT_ALIGNMENT)
+	      enum machine_mode mode = TYPE_MODE (desttype);
+	      if ((mode == BLKmode && STRICT_ALIGNMENT)
+		  || (targetm.slow_unaligned_access (mode, src_align)
+		      && (optab_handler (movmisalign_optab, mode)
+			  == CODE_FOR_nothing)))
 		return false;
 	      srctype = build_aligned_type (TYPE_MAIN_VARIANT (desttype),
 					    src_align);
@@ -1267,7 +1271,11 @@ gimple_fold_builtin_memory_op (gimple_stmt_iterator *gsi,
 	    destvar = fold_build2 (MEM_REF, srctype, dest, off0);
 	  else
 	    {
-	      if (STRICT_ALIGNMENT)
+	      enum machine_mode mode = TYPE_MODE (srctype);
+	      if ((mode == BLKmode && STRICT_ALIGNMENT)
+		  || (targetm.slow_unaligned_access (mode, dest_align)
+		      && (optab_handler (movmisalign_optab, mode)
+			  == CODE_FOR_nothing)))
 		return false;
 	      desttype = build_aligned_type (TYPE_MAIN_VARIANT (srctype),
 					     dest_align);