I am stumped and hope someone more skilled can give me some clues to
solve this problem I have 4.3/4.4 gcc.
I have created RTL define/splits for AVR port logical operation
(AND,IOR etc). These split larger mode operations in to QImode
operations. I also created similar splitters for zero_extend and some
combined zero_extended shift operations.
All of these create QImode moves of subregs and all split before reload
(ie unconditional).
They all split as expected at first oppertunity and produce expected
RTL. Whoppee!
When code involves zero constants (created by zero_extend, or shift) I
can see propagation of constant into following logical operations. (Os
or O3 optimizations). Such as:
Rx = 0
OR Ry,Rx
becoming
OR Ry,0
The propagation is fine, BUT the creation of OR Ry,0 is a totally
redundant operation and remains intact thru all further passes into
final code - apparently not being removed by any optimisations after
split1 pass!
I created RTL pattern to remove these (splitting OR Rx,0 into NOP) and
that removes them - but surely this workaround should not be needed. I
am stumped by what could be causing the problem. Help!
There also seem to be cases where zero constants are not propagated
into instructions. Yet testcase only involves simple operands, no loops
or conditionals or any other side effects that might be reason to block
this. Can anyone suggest some non-obvious reasons for this?
Andy
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