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[PATCH, GCC/ARM, gcc-6-branch] Fix PR80082: LDRD erronously used for 64bit load on ARMv7-R

From: Thomas Preudhomme <thomas dot preudhomme at foss dot arm dot com>
To: Kyrill Tkachov <kyrylo dot tkachov at arm dot com>, Ramana Radhakrishnan <ramana dot radhakrishnan at arm dot com>, Richard Earnshaw <richard dot earnshaw at arm dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
Date: Mon, 27 Mar 2017 12:15:25 +0100
Subject: [PATCH, GCC/ARM, gcc-6-branch] Fix PR80082: LDRD erronously used for 64bit load on ARMv7-R
Authentication-results: sourceware.org; auth=none

Hi,

Currently GCC is happy to use LDRD to perform a 64bit load on ARMv7-R,
as shown by the testcase on this patch. However, LDRD is only atomic
when LPAE extensions is available, which they are not for ARMv7-R. This
commit solve the issue by introducing a new feature bit to distinguish
LPAE extensions instead of deducing it from div instruction
availability.

ChangeLog entries are as follow:

*** gcc/ChangeLog ***

2017-03-22  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	PR target/80082
	* config/arm/arm-protos.h (FL_LPAE): Define macro.
	(FL_FOR_ARCH7VE): Add FL_LPAE.
	(arm_arch_lpae): Declare extern.
	* config/arm/arm.c (arm_arch_lpae): Declare.
	(arm_option_override): Define arm_arch_lpae.
	* config/arm/arm.h (TARGET_HAVE_LPAE): Redefine in term of
	arm_arch_lpae.

*** gcc/testsuite/ChangeLog ***

2017-03-22  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	PR target/80082
	* gcc.target/arm/atomic_loaddi_10.c: New testcase.
	* gcc.target/arm/atomic_loaddi_11.c: Likewise.


Testing: bootstrapped for -march=armv7ve and testsuite shows no regression.

Is this ok for gcc-6-branch?

Best regards,

Thomas

diff --git a/gcc/config/arm/arm-protos.h b/gcc/config/arm/arm-protos.h
index 0083673b161a49e19388c72d3a413aeb481dbfa3..dea00e42551c8295f7e83a72ddb81ae8e9c8e02d 100644
--- a/gcc/config/arm/arm-protos.h
+++ b/gcc/config/arm/arm-protos.h
@@ -360,7 +360,7 @@ extern bool arm_is_constant_pool_ref (rtx);
 #define FL_STRONG     (1 << 8)	      /* StrongARM */
 #define FL_ARCH5E     (1 << 9)        /* DSP extensions to v5 */
 #define FL_XSCALE     (1 << 10)	      /* XScale */
-/* spare	      (1 << 11)	*/
+#define FL_LPAE       (1 << 11)       /* ARMv7-A LPAE.  */
 #define FL_ARCH6      (1 << 12)       /* Architecture rel 6.  Adds
 					 media instructions.  */
 #define FL_VFPV2      (1 << 13)       /* Vector Floating Point V2.  */
@@ -412,7 +412,7 @@ extern bool arm_is_constant_pool_ref (rtx);
 #define FL_FOR_ARCH6M	(FL_FOR_ARCH6 & ~FL_NOTM)
 #define FL_FOR_ARCH7	((FL_FOR_ARCH6T2 & ~FL_NOTM) | FL_ARCH7)
 #define FL_FOR_ARCH7A	(FL_FOR_ARCH7 | FL_NOTM | FL_ARCH6K)
-#define FL_FOR_ARCH7VE	(FL_FOR_ARCH7A | FL_THUMB_DIV | FL_ARM_DIV)
+#define FL_FOR_ARCH7VE	(FL_FOR_ARCH7A | FL_THUMB_DIV | FL_ARM_DIV | FL_LPAE)
 #define FL_FOR_ARCH7R	(FL_FOR_ARCH7A | FL_THUMB_DIV)
 #define FL_FOR_ARCH7M	(FL_FOR_ARCH7 | FL_THUMB_DIV)
 #define FL_FOR_ARCH7EM  (FL_FOR_ARCH7M | FL_ARCH7EM)
@@ -608,6 +608,9 @@ extern int arm_arch_thumb2;
 extern int arm_arch_arm_hwdiv;
 extern int arm_arch_thumb_hwdiv;
 
+/* Nonzero if this chip supports the Large Physical Address Extension.  */
+extern int arm_arch_lpae;
+
 /* Nonzero if chip disallows volatile memory access in IT block.  */
 extern int arm_arch_no_volatile_ce;
 
diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h
index ad123dde991a3e4c4b9563ee6ebb84981767988f..e93ff7f7d8583b653570cbb8605df5a10bfcc6f4 100644
--- a/gcc/config/arm/arm.h
+++ b/gcc/config/arm/arm.h
@@ -254,8 +254,7 @@ extern void (*arm_lang_output_object_attributes_hook)(void);
 #define TARGET_HAVE_LDREX        ((arm_arch6 && TARGET_ARM) || arm_arch7)
 
 /* Nonzero if this chip supports LPAE.  */
-#define TARGET_HAVE_LPAE						\
-  (arm_arch7 && ARM_FSET_HAS_CPU1 (insn_flags, FL_FOR_ARCH7VE))
+#define TARGET_HAVE_LPAE	(arm_arch_lpae)
 
 /* Nonzero if this chip supports ldrex{bh} and strex{bh}.  */
 #define TARGET_HAVE_LDREXBH ((arm_arch6k && TARGET_ARM) || arm_arch7)
diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index c3c89b866355708d91dd2a3dab1e4b33f2215ff8..44bfb53a288f57fbc43a0bd146e193b768d939d2 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -859,6 +859,9 @@ int arm_arch_thumb2;
 int arm_arch_arm_hwdiv;
 int arm_arch_thumb_hwdiv;
 
+/* Nonzero if this chip supports the Large Physical Address Extension.  */
+int arm_arch_lpae;
+
 /* Nonzero if chip disallows volatile memory access in IT block.  */
 int arm_arch_no_volatile_ce;
 
@@ -3181,6 +3184,7 @@ arm_option_override (void)
   arm_arch_iwmmxt2 = ARM_FSET_HAS_CPU1 (insn_flags, FL_IWMMXT2);
   arm_arch_thumb_hwdiv = ARM_FSET_HAS_CPU1 (insn_flags, FL_THUMB_DIV);
   arm_arch_arm_hwdiv = ARM_FSET_HAS_CPU1 (insn_flags, FL_ARM_DIV);
+  arm_arch_lpae = ARM_FSET_HAS_CPU1 (insn_flags, FL_LPAE);
   arm_arch_no_volatile_ce = ARM_FSET_HAS_CPU1 (insn_flags, FL_NO_VOLATILE_CE);
   arm_tune_cortex_a9 = (arm_tune == cortexa9) != 0;
   arm_arch_crc = ARM_FSET_HAS_CPU1 (insn_flags, FL_CRC32);
diff --git a/gcc/testsuite/gcc.target/arm/atomic_loaddi_10.c b/gcc/testsuite/gcc.target/arm/atomic_loaddi_10.c
new file mode 100644
index 0000000000000000000000000000000000000000..ecc3d06d0c9f5966daa3ce7e2d52e09d14e0cbc8
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/atomic_loaddi_10.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target arm_arch_v7ve_ok } */
+/* { dg-options "-O2" } */
+/* { dg-add-options arm_arch_v7ve } */
+
+#include <stdatomic.h>
+
+atomic_llong x = 0;
+
+atomic_llong get_x()
+{
+  return atomic_load(&x);
+}
+
+/* { dg-final { scan-assembler "ldrd" } } */
diff --git a/gcc/testsuite/gcc.target/arm/atomic_loaddi_11.c b/gcc/testsuite/gcc.target/arm/atomic_loaddi_11.c
new file mode 100644
index 0000000000000000000000000000000000000000..85c64ae68b1b1ee68466809f7f83d07ceabec575
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/atomic_loaddi_11.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target arm_arch_v7r_ok } */
+/* { dg-skip-if "do not override -mcpu" { *-*-* } { "-mcpu=*" "-march=*" } { "-mcpu=cortex-r5" } } */
+/* { dg-options "-O2 -mcpu=cortex-r5" } */
+
+#include <stdatomic.h>
+
+atomic_llong x = 0;
+
+atomic_llong get_x()
+{
+  return atomic_load(&x);
+}
+
+/* { dg-final { scan-assembler-not "ldrd" } } */

Follow-Ups:
- Re: [PATCH, GCC/ARM, gcc-6-branch] Fix PR80082: LDRD erronously used for 64bit load on ARMv7-R
  - From: Thomas Preudhomme

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