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parser: Assign value without if-statement

Ruslan Garipov requested to merge ruslangaripov/libxml2:impr/rm_if into master

This avoids an if-statement, because effectively it does nothing. And, for example, binary artifact generated by GCC with -O2 optimization settings does not contain that if-statement -- the code just uses the hprefix->name field explicitly.

Just for fun: a disassembler snippet

The following shows that file libxml2_la-parser.o built before this patch does not contain the if-statement. The file was built by GCC with optimization settings set to -O2.

0000000000006c80 <xmlParseStartTag2.constprop.0>:
    6c80:       41 57                   push   %r15
    ...
    # xmlParseAttribute2() was inlined into xmlParseStartTag2()
    6fe8:       48 8d b4 24 b0 00 00    lea    0xb0(%rsp),%rsi  # hprefix
    6fef:       00 
    6ff0:       4c 89 ff                mov    %r15,%rdi  # ctxt (r15 was assigned above to rbx, which was assigned to ctxt)
    6ff3:       e8 b8 f5 ff ff          call   65b0 <xmlParseQNameHashed>
    ...
    6ffb:       48 89 d5                mov    %rdx,%rbp  # rbp gets hname.name
    6ffe:       48 85 d2                test   %rdx,%rdx
    7001:       0f 84 59 04 00 00       je     7460 <xmlParseStartTag2.constprop.0+0x7e0>
    7007:       49 8b bf 28 02 00 00    mov    0x228(%r15),%rdi  # rdi = ctxt->attsSpecial
    700e:       48 8b 9c 24 b8 00 00    mov    0xb8(%rsp),%rbx  # rbx gets "hprefix + 8 bytes"; this is hprefix->name
    7015:       00                                              # rbx is to be used below as-is, no cmp here or there
    7016:       45 31 f6                xor    %r14d,%r14d
    7019:       48 85 ff                test   %rdi,%rdi
    701c:       74 1e                   je     703c <xmlParseStartTag2.constprop.0+0x3bc>
    701e:       49 89 d0                mov    %rdx,%r8  # hname.name (the 5th argument for xmlHashQLookup2(); 'name' local variable is also not used here as a dedicated object)
    7021:       48 8b 74 24 28          mov    0x28(%rsp),%rsi
    7026:       48 8b 54 24 20          mov    0x20(%rsp),%rdx
    702b:       48 89 d9                mov    %rbx,%rcx  # the 4th argument for xmlHashQLookup2() gets value of hprefix.name field w/o an intermediate local variable 'prefix'.
    702e:       45 31 f6                xor    %r14d,%r14d
    7031:       e8 00 00 00 00          call   7036 <xmlParseStartTag2.constprop.0+0x3b6>  # call xmlHashQLookup2()
    7036:       85 c0                   test   %eax,%eax
    ...

The binary code of the xmlParseStartTag2() function is not changed by the only patch from this request.

No functional changes intended.

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