[sdcc-devel] [ sdcc-Feature Requests-482179 ] Optimization: Track State of ACC & DPTR

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Feature Requests item #482179, was opened at 2001-11-15 18:34
Message generated for change (Comment added) made by frief
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Category: None
Group: None
Status: Open
Priority: 5
Private: No
Submitted By: Geoffrey Yerem (yerem)
Assigned to: Nobody/Anonymous (nobody)
Summary: Optimization: Track State of ACC & DPTR

Initial Comment:
Hi,
    Here's another opportunity for optimization.  In the following code, the compiler doesn't 
recognize that the accumulator (used to store the constant '1') isn't changing.  The same is true 
for the DPTR in the second example.

Geoffrey


xdata volatile char a, b, c, d;

void f2( void )
{
	a = 1; // Accumulator doesn't change.
	b = 1;
	c = 1;
	d = 1;
}

void f3( void )
{
	a = 1; // DPTR doesn't change.
	a = 2;
	a = 3;
	a = 4;
}


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>Comment By: Frieder Ferlemann (frief)
Date: 2007-02-15 12:37

Message:
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Originator: NO

Optimization of f2() is addressed by SDCC 2.6.4 #4634. 

Registers R0..R7 and the accumulator are tracked. 

No tracking of DPTR (and symbols) yet. So while
f3() is three byte shorter there still are multiple 
"mov dptr,#_a" generated for f3().

Set environment variable SDCC_RTRACK to enable
this optimization.

----------------------------------------------------------------------

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