Fix unaligned load with small memcpy on the ARM

store_integral_bit_field is ready to handle BLKmode fields, there is
even a subtlety with their handling on big-endian targets, see e.g.
PR middle-end/50325, but not if they are unaligned, so the fix is
simply to call extract_bit_field for them in order to generate an
unaligned load.  As a bonus, this subsumes  the big-endian specific
path that was added under PR middle-end/50325.

	PR middle-end/92071
	* expmed.c (store_integral_bit_field): For fields larger than a
	word, call extract_bit_field on the value if the mode is BLKmode.
	Remove specific path for big-endian targets and tidy things up a
	little bit.

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index f1a1984e8c744d940ef106b565c00ed58d6f8c12..7b573c07abc38865fcd2c798a34e6ba90b45823b 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2019-03-13  Eric Botcazou  <ebotcazou@adacore.com>
+
+       PR middle-end/92071
+       * expmed.c (store_integral_bit_field): For fields larger than a word,
+       call extract_bit_field on the value if the mode is BLKmode.  Remove
+       specific path for big-endian targets and tidy things up a little bit.
+
 2020-03-12  Richard Sandiford  <richard.sandiford@arm.com>
 
        PR rtl-optimization/90275

diff --git a/gcc/expmed.c b/gcc/expmed.c
index 0461027620941ffb9c00a9ede440521f165b69cd..e7c03fbf92c04b46d7697aad96ad2fa14be4e8e1 100644 (file)
--- a/gcc/expmed.c
+++ b/gcc/expmed.c
@@ -933,8 +933,7 @@ store_integral_bit_field (rtx op0, opt_scalar_int_mode op0_mode,
         However, only do that if the value is not BLKmode.  */
 
       const bool backwards = WORDS_BIG_ENDIAN && fieldmode != BLKmode;
-      unsigned int nwords = (bitsize + (BITS_PER_WORD - 1)) / BITS_PER_WORD;
-      unsigned int i;
+      const int nwords = (bitsize + (BITS_PER_WORD - 1)) / BITS_PER_WORD;
       rtx_insn *last;
 
       /* This is the mode we must force value to, so that there will be enough
@@ -950,35 +949,31 @@ store_integral_bit_field (rtx op0, opt_scalar_int_mode op0_mode,
        value_mode = smallest_int_mode_for_size (nwords * BITS_PER_WORD);
 
       last = get_last_insn ();
-      for (i = 0; i < nwords; i++)
+      for (int i = 0; i < nwords; i++)
        {
-         /* If I is 0, use the low-order word in both field and target;
-            if I is 1, use the next to lowest word; and so on.  */
-         unsigned int wordnum = (backwards
-                                 ? GET_MODE_SIZE (value_mode) / UNITS_PER_WORD
-                                 - i - 1
-                                 : i);
-         unsigned int bit_offset = (backwards ^ reverse
-                                    ? MAX ((int) bitsize - ((int) i + 1)
-                                           * BITS_PER_WORD,
-                                           0)
-                                    : (int) i * BITS_PER_WORD);
-         rtx value_word = operand_subword_force (value, wordnum, value_mode);
-         unsigned HOST_WIDE_INT new_bitsize =
-           MIN (BITS_PER_WORD, bitsize - i * BITS_PER_WORD);
-
-         /* If the remaining chunk doesn't have full wordsize we have
-            to make sure that for big-endian machines the higher order
-            bits are used.  */
-         if (new_bitsize < BITS_PER_WORD && BYTES_BIG_ENDIAN && !backwards)
-           {
-             int shift = BITS_PER_WORD - new_bitsize;
-             rtx shift_rtx = gen_int_shift_amount (word_mode, shift);
-             value_word = simplify_expand_binop (word_mode, lshr_optab,
-                                                 value_word, shift_rtx,
-                                                 NULL_RTX, true,
-                                                 OPTAB_LIB_WIDEN);
-           }
+         /* Number of bits to be stored in this iteration, i.e. BITS_PER_WORD
+            except maybe for the last iteration.  */
+         const unsigned HOST_WIDE_INT new_bitsize
+           = MIN (BITS_PER_WORD, bitsize - i * BITS_PER_WORD);
+         /* Bit offset from the starting bit number in the target.  */
+         const unsigned int bit_offset
+           = backwards ^ reverse
+             ? MAX ((int) bitsize - (i + 1) * BITS_PER_WORD, 0)
+             : i * BITS_PER_WORD;
+         /* Starting word number in the value.  */
+         const unsigned int wordnum
+           = backwards
+             ? GET_MODE_SIZE (value_mode) / UNITS_PER_WORD - (i + 1)
+             : i;
+         /* The chunk of the value in word_mode.  We use bit-field extraction
+             in BLKmode to handle unaligned memory references and to shift the
+             last chunk right on big-endian machines if need be.  */
+         rtx value_word
+           = fieldmode == BLKmode
+             ? extract_bit_field (value, new_bitsize, wordnum * BITS_PER_WORD,
+                                  1, NULL_RTX, word_mode, word_mode, false,
+                                  NULL)
+             : operand_subword_force (value, wordnum, value_mode);
 
          if (!store_bit_field_1 (op0, new_bitsize,
                                  bitnum + bit_offset,

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 6d8eac22c313984f105ad0d5d9146cf6ec22f2af..e695b9bf26f68a936c3c6b5d1032f9079289d617 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2019-03-13  Eric Botcazou  <ebotcazou@adacore.com>
+
+       * gcc.c-torture/compile/20200313-1.c: New test.
+
 2020-03-12  Jeff Law  <law@redhat.com>
 
        PR rtl-optimization/90275

diff --git a/gcc/testsuite/gcc.c-torture/compile/20200313-1.c b/gcc/testsuite/gcc.c-torture/compile/20200313-1.c
new file mode 100644 (file)
index 0000000..4791bad
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/20200313-1.c
@@ -0,0 +1,14 @@
+/* PR middle-end/92071 */
+/* Testcase by David Binderman <dcb314@hotmail.com> */
+
+void *a;
+union U { double c; char d[8]; };
+void bar (union U);
+
+void
+foo (void)
+{
+  union U b;
+  __builtin_memcpy (b.d, a, 8);
+  bar (b);
+}