[sdcc-devel] [ sdcc-Feature Requests-1738430 ] tri-ops again

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Feature Requests item #1738430, was opened at 2007-06-16 19:49
Message generated for change (Comment added) made by maartenbrock
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Category: None
Group: None
Status: Open
Priority: 5
Private: No
Submitted By: Hubert Sack (hsack)
Assigned to: Nobody/Anonymous (nobody)
Summary: tri-ops again

Initial Comment:
I detected in the actual version 4854 that it produces unneeded slocs if the result is a bit and the literals after ? and : are bits too.
I attached a smal source file where it can be reproduced

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>Comment By: Maarten Brock (maartenbrock)
Date: 2007-10-13 11:40

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I ran the regression tests with the exception made by Sandeep disabled and
found something. Have a look at this:

char *str = 1 ? NULL : "never";

When the right side is decorated before the condition is evaluated the
constant string "never" is put in code anyway.
The same is true btw. for the following code.

void foo(void)
{
  char *str = "unused";
}

There is no code generated for the assignment and no space allocated for
str, but the (unused) constant string IS put in the CONST segment.

And that is how one feature request becomes a totally different one.

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Comment By: Maarten Brock (maartenbrock)
Date: 2007-09-06 17:54

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I was looking into this further, but I am stuck now.

The casts on the literals are not yet replaced by a new literal of the
casted type because the ':' part is not decorated yet. And this is done on
purpose by a change to SDCCast.c made by Sandeep in revision 1627. His
comment, which I do not understand, is:

/* delay right side for '?' operator since conditional macro expansions
might rely on this */

Can anyone shed some light on this?

Maarten

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Comment By: Maarten Brock (maartenbrock)
Date: 2007-09-06 14:28

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This should be a more generic request: For any assignment from a tri-op a
temporary is used which most of the time can be avoided. The temporary can
be in registers or an sloc.

Only one special case where the result is a bit and the two operands are
literals is currently optimized.

long i;
char c;
bit b;

void test(unsigned char x)
{
    b = (x<1) ? 1 : 0;              // only this goes without iTemp
    b = (x<2) ? (bit)1 : (bit)0;    // uses a bit sloc
    c = (x<3) ? 1 : 0;              // uses a register
    c = (x<4) ? (char)1 : (char)0;  // uses a register
    i = (x<5) ? 1 : 0;              // uses a register
    i = (x<6) ? (long)1 : (long)0;  // uses several registers
}

Maarten

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