Re: [PATCH] Sanitizing the middle-end interface to the back-end for strict alignment

[Bernd Edlinger <bernd.edlinger@hotmail.de>]

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On 8/15/19 9:47 PM, Bernd Edlinger wrote:
> Hi,
> 
> this is the split out part from the "Fix not 8-byte aligned ldrd/strd on ARMv5 (PR 89544)"
> which is sanitizing the middle-end interface to the back-end for strict alignment,
> and a couple of bug-fixes that are necessary to survive boot-strap.
> It is intended to be applied after the PR 89544 fix.
> 
> I think it would be possible to change the default implementation of STACK_SLOT_ALIGNMENT
> to make all stack variables always naturally aligned instead of doing that only
> in assign_parm_setup_stack, but would still like to avoid changing too many things
> that do not seem to have a problem.  Since this would affect many targets, and more
> kinds of variables that may probably not have a strict alignment problem.
> But I am ready to take your advice though.
> 
> 
> Boot-strapped and reg-tested on x86_64-pc-linux-gnu and arm-linux-gnueabihf
> Is it OK for trunk?
> 
> 

Hmm, actually the hunk in assign_parm_setup_stack is not only failing
an assertion, but rather a wrong code bug:

I found now a test case that generates silently wrong code and is fixed
by this patch.

$ cat unaligned-argument-3.c 
/* { dg-do compile } */
/* { dg-require-effective-target arm_arm_ok } */
/* { dg-options "-marm -mno-unaligned-access -O3" } */

typedef int __attribute__((aligned(1))) s;

void x(char*, s*);
void f(char a, s f)
{
  x(&a, &f);
}

/* { dg-final { scan-assembler-times "str\t\[^\\n\]*\\\[sp\\\]" 1 } } */
/* { dg-final { scan-assembler-times "str\t\[^\\n\]*\\\[sp, #3\\\]" 0 } } */

currently with -marm -mno-unaligned-access -O3 we generate:

f:
	@ args = 0, pretend = 0, frame = 8
	@ frame_needed = 0, uses_anonymous_args = 0
	str	lr, [sp, #-4]!
	sub	sp, sp, #12
	mov	r3, r0
	str	r1, [sp, #3]  <- may trap
	add	r0, sp, #7
	add	r1, sp, #3
	strb	r3, [sp, #7]
	bl	x
	add	sp, sp, #12
	@ sp needed
	ldr	pc, [sp], #4


So I would like to add a test case to the patch as attached.

Tested with a cross, that both dg-final fail currently and are fixed
with the other patches applied.

Is it OK for trunk?


Thanks
Bernd.

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2019-08-17  Bernd Edlinger  <bernd.edlinger@hotmail.de>

	PR middle-end/89544
	* gcc.target/arm/unaligned-argument-3.c: New test.

Index: gcc/testsuite/gcc.target/arm/unaligned-argument-3.c
===================================================================
--- gcc/testsuite/gcc.target/arm/unaligned-argument-3.c	(revision 0)
+++ gcc/testsuite/gcc.target/arm/unaligned-argument-3.c	(working copy)
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target arm_arm_ok } */
+/* { dg-options "-marm -mno-unaligned-access -O3" } */
+
+typedef int __attribute__((aligned(1))) s;
+
+void x(char*, s*);
+void f(char a, s f)
+{
+  x(&a, &f);
+}
+
+/* { dg-final { scan-assembler-times "str\t\[^\\n\]*\\\[sp\\\]" 1 } } */
+/* { dg-final { scan-assembler-times "str\t\[^\\n\]*\\\[sp, #3\\\]" 0 } } */