rtlanal: Another fix for VOIDmode MEMs [PR98601]

This is a sequel to the PR85022 changes, inline-asm can (unfortunately)
introduce VOIDmode MEMs and in PR85022 they have been changed so that
we don't pretend we know their size (as opposed to assuming they have
zero size).

This time we ICE in rtx_addr_can_trap_p_1 because it assumes that
all memory but BLKmode has known size.  The patch just treats VOIDmode
MEMs like BLKmode in that regard.  And, the STRICT_ALIGNMENT change
is needed because VOIDmode has GET_MODE_SIZE of 0 and we don't want to
check if something is a multiple of 0.

2021-04-10  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/98601
	* rtlanal.c (rtx_addr_can_trap_p_1): Allow in assert unknown size
	not just for BLKmode, but also for VOIDmode.  For STRICT_ALIGNMENT
	unaligned_mems handle VOIDmode like BLKmode.

	* gcc.dg/torture/pr98601.c: New test.

gcc/rtlanal.c

@@ -464,12 +464,17 @@ rtx_addr_can_trap_p_1 (const_rtx x, poly_int64 offset, poly_int64 size,
 		       machine_mode mode, bool unaligned_mems)
 {
   enum rtx_code code = GET_CODE (x);
-  gcc_checking_assert (mode == BLKmode || known_size_p (size));
+  gcc_checking_assert (mode == BLKmode
+		       || mode == VOIDmode
+		       || known_size_p (size));
   poly_int64 const_x1;
 
   /* The offset must be a multiple of the mode size if we are considering
      unaligned memory references on strict alignment machines.  */
-  if (STRICT_ALIGNMENT && unaligned_mems && mode != BLKmode)
+  if (STRICT_ALIGNMENT
+      && unaligned_mems
+      && mode != BLKmode
+      && mode != VOIDmode)
     {
       poly_int64 actual_offset = offset;
 

gcc/testsuite/gcc.dg/torture/pr98601.c

@@ -0,0 +1,14 @@
+/* PR rtl-optimization/98601 */
+/* { dg-do compile } */
+
+void
+foo (void *p)
+{
+  asm ("" : "=m" (*p));			/* { dg-warning "dereferencing 'void \\*' pointer" } */
+}
+
+void
+bar (void *p)
+{
+  asm volatile ("" : : "m" (*p));	/* { dg-warning "dereferencing 'void \\*' pointer" } */
+}