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[backported,v5,v6] Fix PR71976 in combine.c:get_last_value()

Message ID 4767bd39-f99b-cc6b-90f6-117fc4aefcc2@gjlay.de
State New
Headers show

Commit Message

Georg-Johann Lay Aug. 8, 2016, 11:11 a.m. UTC 
Applied to

v5: https://gcc.gnu.org/r239239
v6: https://gcc.gnu.org/r239238

Johann

	Backport from 2016-07-29 trunk r238863.

	PR rtl-optimization/71976
	* combine.c (get_last_value): Return 0 if the argument for which
	the function is called has a wider mode than the recorded value.



On 29.07.2016 11:19, Segher Boessenkool wrote:
> On Fri, Jul 29, 2016 at 10:56:22AM +0200, Georg-Johann Lay wrote:
>> The issue with wrong-code bug PR71976 is that combine.c:get_last_value was
>> called for a hard register in a wider mode (DImode) than the stored value
>> had (QImode).  The patch introduces a test of the mode precision and only
>> returns the recorded value if the according mode is not smaller than the
>> mode for which get_last_value is called.
>>
>> Segher already tested the patch on 32 different (sub-)architectures of
>> Linux without any regression, cf.
>>
>> https://gcc.gnu.org/ml/gcc/2016-07/msg00215.html
>>
>> Ok for trunk and to backport?
>
> Okay for trunk, okay for backport after a week or so.
>
> Thanks!
>
>
> Segher
diff mbox

Patch

Index: combine.c
===================================================================
--- combine.c	(revision 238849)
+++ combine.c	(working copy)
@@ -13210,6 +13210,12 @@  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;