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Re: [PATCHv5] Fix not 8-byte aligned ldrd/strd on ARMv5 (PR 89544)

On 04/09/2019 14:28, Bernd Edlinger wrote:
On 9/4/19 2:53 PM, Richard Earnshaw (lists) wrote:
On 15/08/2019 20:47, Bernd Edlinger wrote:
On 8/15/19 6:29 PM, Richard Biener wrote:

Please split it into the parts for the PR and parts making the
asserts not trigger.

Yes, will do.

Okay, here is the rest of the PR 89544 fix,
actually just an optimization, making the larger stack alignment
known to the middle-end, and the test cases.

Boot-strapped and reg-tested on x86_64-pc-linux-gnu and arm-linux-gnueabihf.
Is it OK for trunk?


Index: gcc/testsuite/
--- gcc/testsuite/    (Revision 0)
+++ gcc/testsuite/    (Arbeitskopie)
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target arm_arm_ok } */
+/* { dg-require-effective-target arm_ldrd_strd_ok } */
+/* { dg-options "-marm -mno-unaligned-access -O3" } */
+struct s {
+  int a, b;
+} __attribute__((aligned(8)));
+struct s f0;
+void f(int a, int b, int c, int d, int e, struct s f)
+  f0 = f;
+/* { dg-final { scan-assembler-times "ldrd" 0 } } */
+/* { dg-final { scan-assembler-times "strd" 0 } } */
+/* { dg-final { scan-assembler-times "stm" 1 } } */

I don't think this test is right.  While we can't use an LDRD to load the argument off the stack, there's nothing wrong with using an STRD to then store the value to f0 (as that is 8-byte aligned).  So the second and third scan-assembler tests are meaningless.

Ah, that is very similar to the unaligned-memcpy-2/3.c,

initially that is a movdi,
then in subreg1 it is split in two movsi
which is then re-assembled as ldm

Not sure if that is intended in that way.

Yeah, these are causing me some problems too, but that's because with some changes I'm working on I now see the compiler using r4 and r5, which leads to prologue and epilogue stores that distort the results.

Tests like this are generally fragile - I hate 'em!!!!


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