ARM: Fix conditional execution [PR113915]

By default most patterns can be conditionalized on Arm targets.  However
Thumb-2 predication requires the "predicable" attribute be explicitly
set to "yes".  Most patterns are shared between Arm and Thumb(-2) and are
marked with "predicable".  Given this sharing, it does not make sense to
use a different default for Arm.  So only consider conditional execution
of instructions that have the predicable attribute set to yes.  This ensures
that patterns not explicitly marked as such are never conditionally executed.

gcc/ChangeLog:
	PR target/113915
	* config/arm/arm.md (NOCOND): Improve comment.
	(arm_rev*) Add predicable.
	* config/arm/arm.cc (arm_final_prescan_insn): Add check for
	PREDICABLE_YES.

gcc/testsuite/ChangeLog:
	PR target/113915
	* gcc.target/arm/builtin-bswap-1.c: Fix test to allow conditional
	execution both for Arm and Thumb-2.

3 files changed, 15 insertions, 11 deletions

diff --git a/gcc/config/arm/arm.cc b/gcc/config/arm/arm.cc
index 1cd6926..6a35fe4 100644
--- a/gcc/config/arm/arm.cc
+++ b/gcc/config/arm/arm.cc
@@ -25613,11 +25613,12 @@ arm_final_prescan_insn (rtx_insn *insn)
 	      break;
 
 	    case INSN:
-	      /* Instructions using or affecting the condition codes make it
-		 fail.  */
+	      /* Check the instruction is explicitly marked as predicable.
+		 Instructions using or affecting the condition codes are not.  */
 	      scanbody = PATTERN (this_insn);
 	      if (!(GET_CODE (scanbody) == SET
 		    || GET_CODE (scanbody) == PARALLEL)
+		  || get_attr_predicable (this_insn) != PREDICABLE_YES
 		  || get_attr_conds (this_insn) != CONDS_NOCOND)
 		fail = TRUE;
 	      break;
diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md
index 814e871..1fd0014 100644
--- a/gcc/config/arm/arm.md
+++ b/gcc/config/arm/arm.md
@@ -319,6 +319,8 @@
 ;
 ; NOCOND means that the instruction does not use or alter the condition
 ;   codes but can be converted into a conditionally exectuted instruction.
+;   Given that NOCOND is the default for most instructions if omitted,
+;   the attribute predicable must be set to yes as well.
 
 (define_attr "conds" "use,set,clob,unconditional,nocond"
 	(if_then_else
@@ -12559,6 +12561,7 @@
   revsh%?\t%0, %1"
   [(set_attr "arch" "t1,t2,32")
    (set_attr "length" "2,2,4")
+   (set_attr "predicable" "no,yes,yes")
    (set_attr "type" "rev")]
 )
 
@@ -12572,6 +12575,7 @@
    rev16%?\t%0, %1"
   [(set_attr "arch" "t1,t2,32")
    (set_attr "length" "2,2,4")
+   (set_attr "predicable" "no,yes,yes")
    (set_attr "type" "rev")]
 )
 
@@ -12596,6 +12600,7 @@
    rev16%?\t%0, %1"
   [(set_attr "arch" "t1,t2,32")
    (set_attr "length" "2,2,4")
+   (set_attr "predicable" "no,yes,yes")
    (set_attr "type" "rev")]
 )
 
@@ -12616,6 +12621,7 @@
    rev16%?\t%0, %1"
   [(set_attr "arch" "t1,t2,32")
    (set_attr "length" "2,2,4")
+   (set_attr "predicable" "no,yes,yes")
    (set_attr "type" "rev")]
 )
 
diff --git a/gcc/testsuite/gcc.target/arm/builtin-bswap-1.c b/gcc/testsuite/gcc.target/arm/builtin-bswap-1.c
index c1e7740..1a311a6 100644
--- a/gcc/testsuite/gcc.target/arm/builtin-bswap-1.c
+++ b/gcc/testsuite/gcc.target/arm/builtin-bswap-1.c
@@ -5,14 +5,11 @@
    of the instructions.  Add an -mtune option known to facilitate that.  */
 /* { dg-additional-options "-O2 -mtune=cortex-a53" } */
 /* { dg-final { scan-assembler-not "orr\[ \t\]" } } */
-/* { dg-final { scan-assembler-times "revsh\\t" 1 { target { arm_nothumb } } } }  */
-/* { dg-final { scan-assembler-times "revshne\\t" 1 { target { arm_nothumb } } } }  */
-/* { dg-final { scan-assembler-times "revsh\\t" 2 { target { ! arm_nothumb } } } }  */
-/* { dg-final { scan-assembler-times "rev16\\t" 1 { target { arm_nothumb } } } }  */
-/* { dg-final { scan-assembler-times "rev16ne\\t" 1 { target { arm_nothumb } } } }  */
-/* { dg-final { scan-assembler-times "rev16\\t" 2 { target { ! arm_nothumb } } } }  */
-/* { dg-final { scan-assembler-times "rev\\t" 2 { target { arm_nothumb } } } }  */
-/* { dg-final { scan-assembler-times "revne\\t" 2 { target { arm_nothumb } } } }  */
-/* { dg-final { scan-assembler-times "rev\\t" 4 { target { ! arm_nothumb } } } }  */
+/* { dg-final { scan-assembler-times "revsh\\t" 1 } }  */
+/* { dg-final { scan-assembler-times "revshne\\t" 1 } }  */
+/* { dg-final { scan-assembler-times "rev16\\t" 1 } }  */
+/* { dg-final { scan-assembler-times "rev16ne\\t" 1 } }  */
+/* { dg-final { scan-assembler-times "rev\\t" 2 } }  */
+/* { dg-final { scan-assembler-times "revne\\t" 2 } }  */
 
 #include "builtin-bswap.x"