trAvis - MANAGER

Edit File: opt_var.txt

NASM Optimizer Usage of Certain Variables to Control Assembly prepared by: John R Coffman date: 07-Mar-2005 GLOBAL variables: optimizing -1 flags nasm 0.98 compatible operation; offsets usually are explicit (short/near) no optimization passes 0 flags non-optimized assembly; forward references generate long offsets; always assembles no optimization passes 2 or more specifies optmization passes. 5 is the actual recommended minimum setting optimization passes (2 or more, plus passes 1 and 2 will be required) pass0 0 flags an optimizer pass (multiple passes) 1 flags pass1 (define labels) 2 flags pass2 (spit out code) LOCAL variables: local to 'assemble_file' (nasm.c) pass_max 2 for non-optimized assembly 4 or more for optimized assembly pass index of the FOR loop (1..pass_max) with optimized assembly, this variable is advanced to 'pass_max - 1' in the logic at the end of the loop to terminate an optimized assembly before all passes are used; i.e., when convergence has occurred pass1 flag for making parts of the assembler do pass 1 behaviors on optimizer passes pass2 flag for making parts of the assembler do pass 2 behaviors on optimizer passes pass_cnt benign counter for counting the actual number of passes taken. Since 'pass' may be jerked upward early on optimized assembly, it does not accurately reflect the number of passes taken. always ends at 2 for non-optimized assembly How the variables sequence: NON-OPTIMIZED assembly: pass0 1 2 all indicate, pass 1 and pass 2 pass1 1 2 pass2 1 2 pass 1 2 ---------------------------------------- pass_max pre-set to 2 pass_cnt ends at 2 OPTIMIZED assembly: optimizing set to 2 or greater pass0 0 0 0 0 0 ... 0 0 1 2 pass1 1 1 1 1 1 ... 1 1 1 2 pass2 1 2 2 2 2 ... 2 2 2 2 pass 1 2 3 4 5 ... 7 8 9 12 pass_max pre-set to, say, 12 pass_cnt ends at 10 for this assembly >From pass_cnt, the reported number of passes will be 1+8+1, meaning 8 optimization passes, plus pass 1, plus pass 2. Subroutines may check 'pass0' to see if an optimizer pass is in progress (pass0==0). Many have arguments to tell what pass is in progress. But these variables are passed in as 'pass1' or 'pass2'. >From the sequences above, 'pass' bears no relation to the desired pass 1 or pass 2 behavior of the assembler. 'pass1' is used to tell parts of the assembler, on multiple occasions, that pass 1 is in progress, and only once that pass 2 is being performed. Other parts of the assembler need to be told only once that pass 1 is being performed, but may be told multiple times that pass 2 is being done. For instance, the preprocessor reset operation looks at pass1, and it thinks many pass 1 resets are being done, but only one pass 2 reset is done. Also, certain errors are non-fatal on pass 1, but fatal on pass 2; hence, they are tied to the 'pass1' variable to determine the assembler pass number. Further, segment definitions look at the 'pass2' variable, since they do some initialization on pass 1, but are pretty much no-ops on pass 2. Hence, they should see pass 1 only once, but may see pass 2 multiple times. [end]