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 --git a/gcc/gimple-fold.cc b/gcc/gimple-fold.cc
index c9179ab..5eff7d6 100644 (file)
--- 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);