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RFA: Fix middle-end/44769
- From: Joern Rennecke <amylaar at spamcop dot net>
- To: gcc-patches at gcc dot gnu dot org
- Date: Wed, 10 Nov 2010 11:55:45 -0500
- Subject: RFA: Fix middle-end/44769
Bootstrapping on i686-pc-linux-gnu.
We get the warnings for code that is dead, but the warnings get emitted
anyways because we use effectively if (0) rather than #if 0.
By assigning the shift count to a variable first, we can avoid the
warning for the dead code.
Although we could split the shift or use a conditional, that doesn't
look that good an option here, because BITS_PER_WORD is not always
a constant; for some targets, it depends on a gcc option.
So far, we've evaluated BITS_PER_WORD in this piece of code twice.
Using a split shift or a conditional, we'd evaluate it at least four times.
Moreover, for a split shift count, we'd have the added awkwardness
what to do to make it safe for future targets with add BITS_PER_WORD
(not counting 36, 20 or 22 as odd in this context ;-).
By assigning BITS_PER_UNIT to a variable first, we evaluate it only once.
2010-11-10 Joern Rennecke <firstname.lastname@example.org>
* final.c (split_double): Don't use BITS_PER_WORD directly in
--- final.c (revision 166491)
+++ final.c (working copy)
@@ -3807,10 +3807,11 @@ split_double (rtx value, rtx *first, rtx
Sign extend each half to HOST_WIDE_INT. */
unsigned HOST_WIDE_INT low, high;
unsigned HOST_WIDE_INT mask, sign_bit, sign_extend;
+ unsigned bits_per_word = BITS_PER_WORD;
/* Set sign_bit to the most significant bit of a word. */
sign_bit = 1;
- sign_bit <<= BITS_PER_WORD - 1;
+ sign_bit <<= bits_per_word - 1;
/* Set mask so that all bits of the word are set. We could
have used 1 << BITS_PER_WORD instead of basing the
@@ -3833,7 +3834,7 @@ split_double (rtx value, rtx *first, rtx
/* Pick the higher word, shifted to the least significant
bits, and sign-extend it. */
high = INTVAL (value);
- high >>= BITS_PER_WORD - 1;
+ high >>= bits_per_word - 1;
high >>= 1;
high &= mask;
if (high & sign_bit)