On Thu, Jan 03, 2019 at 07:03:59PM +0000, Richard Sandiford wrote:
> Richard Sandiford <richard.sandif...@arm.com> writes:
> > This still seems risky and isn't what the name and function comment
OK, how about this delta from the previous patch to ameliorate the
maintenance risk?
diff --git a/gcc/genattrtab.c b/gcc/genattrtab.c
index c86b3587cd9..2a81445a160 100644
--- a/gcc/genattrtab.c
+++ b/gcc/genattrtab.c
@@ -3750,8 +3750,9 @@ write_test_expr (FILE *outf, rtx exp, unsigned int
attrs_cached, int flags,
return attrs_cached;
}
-/* Given an attribute value, return the maximum CONST_INT or CONST_STRING
- argument encountered. Return INT_MAX if the value is unknown. */
+/* Given an attribute value expression, return the maximum value that
+ might be evaluated assuming all conditionals are independent.
+ Return INT_MAX if the value can't be calculated by this function. */
static int
max_attr_value (rtx exp)
@@ -3805,8 +3806,9 @@ max_attr_value (rtx exp)
return current_max;
}
-/* Given an attribute value, return the minimum CONST_INT or CONST_STRING
- argument encountered. Return INT_MIN if the value is unknown. */
+/* Given an attribute value expression, return the minimum value that
+ might be evaluated assuming all conditionals are independent.
+ Return INT_MIN if the value can't be calculated by this function. */
static int
min_attr_value (rtx exp)
@@ -3860,9 +3862,18 @@ min_attr_value (rtx exp)
return current_min;
}
-/* Given an attribute value, return the result of ORing together all
- CONST_INT or CONST_STRING arguments encountered. Return -1 if the
- numeric value is not known. */
+/* Given an attribute value expression, return the result of ORing
+ together all CONST_INT or CONST_STRING arguments encountered in the
+ value parts of the expression. (ie. excluding those that might be
+ found in condition expressions of COND or IF_THEN_ELSE.) Note that
+ this isn't the same as the OR of all possible evaluations of the
+ expression, but is sufficient for the current use of this function
+ in calculating the largest power of two that divides insn lengths.
+ ie. We are calculating a property of the underlying machine
+ instructions emitted by gcc. In particular this implementation
+ assumes conditionals are independent and that the operands of a
+ PLUS are multiples of the underlying machine instruction length.
+ Returns -1 if the value can't be calculated by this function. */
static int
or_attr_value (rtx exp)
@@ -3882,13 +3893,7 @@ or_attr_value (rtx exp)
case PLUS:
current_or = or_attr_value (XEXP (exp, 0));
- if (current_or != -1)
- {
- int n = current_or;
- current_or = or_attr_value (XEXP (exp, 1));
- if (current_or != -1)
- current_or += n;
- }
+ current_or |= or_attr_value (XEXP (exp, 1));
break;
case COND:
