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Re: Need help with PR71976 combine.c::get_last_value returns a wrong result


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


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