avr-gcc: README added

[Michael Baeuerle <micha%NetBSD.org@localhost>]

Module Name:	pkgsrc-wip
Committed By:	Michael Baeuerle <micha%NetBSD.org@localhost>
Pushed By:	micha
Date:		Mon Jun 20 16:18:23 2022 +0200
Changeset:	019770bf333587fcbfbf9ad9ff5abec7b6852fd1

Added Files:
	avr-gcc/README

Log Message:
avr-gcc: README added

To see a diff of this commit:
https://wip.pkgsrc.org/cgi-bin/gitweb.cgi?p=pkgsrc-wip.git;a=commitdiff;h=019770bf333587fcbfbf9ad9ff5abec7b6852fd1

Please note that diffs are not public domain; they are subject to the
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diffstat:
 avr-gcc/README | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diffs:
diff --git a/avr-gcc/README b/avr-gcc/README
new file mode 100644
index 0000000000..a7063c2492
--- /dev/null
+++ b/avr-gcc/README
@@ -0,0 +1,24 @@
+If you get errors like:
+
+    [...] error: array subscript 0 is outside array bounds [...]
+
+use the workaround from this bug ticket:
+<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105523>
+
+    --param=min-pagesize=0
+
+The optimization for size is worse compared with GCC 10, even with -Oz.
+If the code uses interrupt handlers use:
+
+    -mcall-prologues
+
+The defaults for branch cost and reorder algorithm may produce larger code.
+Sometimes the following options give better results:
+
+    -mbranch-cost=10
+    -freorder-blocks-algorithm=stc
+
+Do not use type int for 8-Bit values. Even for static functions the optimizer
+may not detect that the additional bits will always be zero.
+
+(Optimization for size tested with ATtiny88)