+static tree chrec_convert_1 (tree, tree, gimple, bool);
+
+/* Converts BASE and STEP of affine scev to TYPE. LOOP is the loop whose iv
+ the scev corresponds to. AT_STMT is the statement at that the scev is
+ evaluated. USE_OVERFLOW_SEMANTICS is true if this function should assume that
+ the rules for overflow of the given language apply (e.g., that signed
+ arithmetics in C does not overflow) -- i.e., to use them to avoid unnecessary
+ tests, but also to enforce that the result follows them. Returns true if the
+ conversion succeeded, false otherwise. */
+
+bool
+convert_affine_scev (struct loop *loop, tree type,
+ tree *base, tree *step, gimple at_stmt,
+ bool use_overflow_semantics)
+{
+ tree ct = TREE_TYPE (*step);
+ bool enforce_overflow_semantics;
+ bool must_check_src_overflow, must_check_rslt_overflow;
+ tree new_base, new_step;
+ tree step_type = POINTER_TYPE_P (type) ? sizetype : type;
+
+ /* In general,
+ (TYPE) (BASE + STEP * i) = (TYPE) BASE + (TYPE -- sign extend) STEP * i,
+ but we must check some assumptions.
+
+ 1) If [BASE, +, STEP] wraps, the equation is not valid when precision
+ of CT is smaller than the precision of TYPE. For example, when we
+ cast unsigned char [254, +, 1] to unsigned, the values on left side
+ are 254, 255, 0, 1, ..., but those on the right side are
+ 254, 255, 256, 257, ...
+ 2) In case that we must also preserve the fact that signed ivs do not
+ overflow, we must additionally check that the new iv does not wrap.
+ For example, unsigned char [125, +, 1] casted to signed char could
+ become a wrapping variable with values 125, 126, 127, -128, -127, ...,
+ which would confuse optimizers that assume that this does not
+ happen. */
+ must_check_src_overflow = TYPE_PRECISION (ct) < TYPE_PRECISION (type);
+
+ enforce_overflow_semantics = (use_overflow_semantics
+ && nowrap_type_p (type));
+ if (enforce_overflow_semantics)
+ {
+ /* We can avoid checking whether the result overflows in the following
+ cases:
+
+ -- must_check_src_overflow is true, and the range of TYPE is superset
+ of the range of CT -- i.e., in all cases except if CT signed and
+ TYPE unsigned.
+ -- both CT and TYPE have the same precision and signedness, and we
+ verify instead that the source does not overflow (this may be
+ easier than verifying it for the result, as we may use the
+ information about the semantics of overflow in CT). */
+ if (must_check_src_overflow)
+ {
+ if (TYPE_UNSIGNED (type) && !TYPE_UNSIGNED (ct))
+ must_check_rslt_overflow = true;
+ else
+ must_check_rslt_overflow = false;
+ }
+ else if (TYPE_UNSIGNED (ct) == TYPE_UNSIGNED (type)
+ && TYPE_PRECISION (ct) == TYPE_PRECISION (type))
+ {
+ must_check_rslt_overflow = false;
+ must_check_src_overflow = true;
+ }
+ else
+ must_check_rslt_overflow = true;
+ }
+ else
+ must_check_rslt_overflow = false;
+
+ if (must_check_src_overflow
+ && scev_probably_wraps_p (*base, *step, at_stmt, loop,
+ use_overflow_semantics))
+ return false;
+
+ new_base = chrec_convert_1 (type, *base, at_stmt,
+ use_overflow_semantics);
+ /* The step must be sign extended, regardless of the signedness
+ of CT and TYPE. This only needs to be handled specially when
+ CT is unsigned -- to avoid e.g. unsigned char [100, +, 255]
+ (with values 100, 99, 98, ...) from becoming signed or unsigned
+ [100, +, 255] with values 100, 355, ...; the sign-extension is
+ performed by default when CT is signed. */
+ new_step = *step;
+ if (TYPE_PRECISION (step_type) > TYPE_PRECISION (ct) && TYPE_UNSIGNED (ct))
+ new_step = chrec_convert_1 (signed_type_for (ct), new_step, at_stmt,
+ use_overflow_semantics);
+ new_step = chrec_convert_1 (step_type, new_step, at_stmt, use_overflow_semantics);
+
+ if (automatically_generated_chrec_p (new_base)
+ || automatically_generated_chrec_p (new_step))
+ return false;
+
+ if (must_check_rslt_overflow
+ /* Note that in this case we cannot use the fact that signed variables
+ do not overflow, as this is what we are verifying for the new iv. */
+ && scev_probably_wraps_p (new_base, new_step, at_stmt, loop, false))
+ return false;
+
+ *base = new_base;
+ *step = new_step;
+ return true;
+}
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