Hi Johann,
I tested a variant of your patch, building Linux for 32 different
(sub-)architectures; surprisingly (to me) there are no regressions
at all.
Do you want to send it to gcc-patches?
Segher
diff --git a/gcc/combine.c b/gcc/combine.c
index 77e0d2b..750bf83 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -13240,6 +13240,12 @@ get_last_value (const_rtx x)
&& DF_INSN_LUID (rsp->last_set) >= subst_low_luid)
return 0;
+ /* If fewer bits were set than what we are asked for now, we cannot use
+ the value. */
+ if (GET_MODE_PRECISION (rsp->last_set_mode)
+ < GET_MODE_PRECISION (GET_MODE (x)))
+ return 0;
+
/* If the value has all its registers valid, return it. */
if (get_last_value_validate (&value, rsp->last_set, rsp->last_set_label, 0))
return value;
--
1.9.3
