Patchwork [ARM] Fix broken shift patterns

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Submitter Andrew Stubbs
Date Oct. 7, 2011, 3:05 p.m.
Message ID <4E8F154E.90208@codesourcery.com>
Download mbox | patch
Permalink /patch/118329/
State New
Headers show

Comments

Andrew Stubbs - Oct. 7, 2011, 3:05 p.m.
On 07/10/11 13:37, Paul Brook wrote:
>> Done, and attached.
>
> Ok.
>
> Two changes to the testcase that I'll pre-approve:
> - Add a comment along the lines of
>    /* ARM has shift-and-alu insns.  Depending on the ALU op GCC represents some
>     of these as a left shift, others as a multiply.  Check that we match the
>     right one.  */
> - Also test (a * 64) - b [rsb] and ~(a * 64) [mvn]

Thanks, I've committed the attached.

>> In this case, I believe the hardware simply shifts the the value clean
>> out of the register, and always returns a zero (or maybe -1 for
>> ashiftrt?).
>
> I'm not convinced.  ARM instructions shift modulo 256
> (i.e. a>>  (b&  0xff).  I'm pretty sure anything that gets constant-folded by
> earlier passes will not honor these semantics.

True, but I'm still not sure what the least wrong way to do this might be.

>>> For bonus points we should probably disallow MULT in the arm_shiftsi3
>>> pattern, stop it interacting with the regular mulsi3 pattern in
>>> undesirable ways.
>>
>> How might that be a problem? Is it not the case that canonical forms
>> already deals with this?
>
> Mainly just general principle that having two insns with the same pattern is
> wrong - reload can't flip between them like it can different altrnatives, and
> there's obscure rules about which one wins when both match.

OK, so we'd just need a shift_operator_that_isnt_mult predicate, 
(probably not with that name).

Andrew

Patch

2011-10-07  Andrew Stubbs  <ams@codesourcery.com>

	gcc/
	* config/arm/predicates.md (shift_amount_operand): Remove constant
	range check.
	(shift_operator): Check range of constants for all shift operators.

	gcc/testsuite/
	* gcc.dg/pr50193-1.c: New file.
	* gcc.target/arm/shiftable.c: New file.

--- a/gcc/config/arm/predicates.md
+++ b/gcc/config/arm/predicates.md
@@ -129,11 +129,12 @@ 
   (ior (match_operand 0 "arm_rhs_operand")
        (match_operand 0 "memory_operand")))
 
+;; This doesn't have to do much because the constant is already checked
+;; in the shift_operator predicate.
 (define_predicate "shift_amount_operand"
   (ior (and (match_test "TARGET_ARM")
 	    (match_operand 0 "s_register_operand"))
-       (and (match_code "const_int")
-	    (match_test "((unsigned HOST_WIDE_INT) INTVAL (op)) < 32"))))
+       (match_operand 0 "const_int_operand")))
 
 (define_predicate "arm_add_operand"
   (ior (match_operand 0 "arm_rhs_operand")
@@ -219,13 +220,20 @@ 
        (match_test "mode == GET_MODE (op)")))
 
 ;; True for shift operators.
+;; Notes:
+;;  * mult is only permitted with a constant shift amount
+;;  * patterns that permit register shift amounts only in ARM mode use
+;;    shift_amount_operand, patterns that always allow registers do not,
+;;    so we don't have to worry about that sort of thing here.
 (define_special_predicate "shift_operator"
   (and (ior (ior (and (match_code "mult")
 		      (match_test "power_of_two_operand (XEXP (op, 1), mode)"))
 		 (and (match_code "rotate")
 		      (match_test "GET_CODE (XEXP (op, 1)) == CONST_INT
 				   && ((unsigned HOST_WIDE_INT) INTVAL (XEXP (op, 1))) < 32")))
-	    (match_code "ashift,ashiftrt,lshiftrt,rotatert"))
+	    (and (match_code "ashift,ashiftrt,lshiftrt,rotatert")
+		 (match_test "GET_CODE (XEXP (op, 1)) != CONST_INT
+			      || ((unsigned HOST_WIDE_INT) INTVAL (XEXP (op, 1))) < 32")))
        (match_test "mode == GET_MODE (op)")))
 
 ;; True for shift operators which can be used with saturation instructions.
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr50193-1.c
@@ -0,0 +1,10 @@ 
+/* PR 50193: ARM: ICE on a | (b << negative-constant) */
+/* Ensure that the compiler doesn't ICE.  */
+
+/* { dg-options "-O2" } */
+
+int
+foo(int a, int b)
+{
+  return a | (b << -3); /* { dg-warning "left shift count is negative" } */
+}
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/shiftable.c
@@ -0,0 +1,63 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-require-effective-target arm32 } */
+
+/* ARM has shift-and-alu insns.  Depending on the ALU op GCC represents some
+   of these as a left shift, others as a multiply.  Check that we match the
+    right one.  */
+
+int
+plus (int a, int b)
+{
+  return (a * 64) + b;
+}
+
+/* { dg-final { scan-assembler "add.*\[al]sl #6" } } */
+
+int
+minus (int a, int b)
+{
+  return a - (b * 64);
+}
+
+/* { dg-final { scan-assembler "sub.*\[al]sl #6" } } */
+
+int
+ior (int a, int b)
+{
+  return (a * 64) | b;
+}
+
+/* { dg-final { scan-assembler "orr.*\[al]sl #6" } } */
+
+int
+xor (int a, int b)
+{
+  return (a * 64) ^ b;
+}
+
+/* { dg-final { scan-assembler "eor.*\[al]sl #6" } } */
+
+int
+and (int a, int b)
+{
+  return (a * 64) & b;
+}
+
+/* { dg-final { scan-assembler "and.*\[al]sl #6" } } */
+
+int
+rsb (int a, int b)
+{
+  return (a * 64) - b;
+}
+
+/* { dg-final { scan-assembler "rsb.*\[al]sl #6" } } */
+
+int
+mvn (int a, int b)
+{
+  return ~(a * 64);
+}
+
+/* { dg-final { scan-assembler "mvn.*\[al]sl #6" } } */