[LLVMbugs] [Bug 7748] New: VC++ truncates X86II::VEX enum constants

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=7748

           Summary: VC++ truncates X86II::VEX enum constants
           Product: new-bugs
           Version: trunk
          Platform: PC
        OS/Version: Windows XP
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: dimitry at andric.com
                CC: llvmbugs at cs.uiuc.edu


During compilation with VC++ 9 of several llvm files that include
X86InstInfo.h, I am getting the following warnings about it:

lib\target\x86\X86InstrInfo.h(442) : warning C4341: 'VEX' : signed value is out
of range for enum constant
lib\target\x86\X86InstrInfo.h(442) : warning C4309: 'initializing' : truncation
of constant value
lib\target\x86\X86InstrInfo.h(446) : warning C4341: 'VEX_W' : signed value is
out of range for enum constant
lib\target\x86\X86InstrInfo.h(446) : warning C4309: 'initializing' : truncation
of constant value
lib\target\x86\X86InstrInfo.h(451) : warning C4341: 'VEX_4V' : signed value is
out of range for enum constant
lib\target\x86\X86InstrInfo.h(451) : warning C4309: 'initializing' : truncation
of constant value
lib\target\x86\X86InstrInfo.h(456) : warning C4341: 'VEX_I8IMM' : signed value
is out of range for enum constant
lib\target\x86\X86InstrInfo.h(456) : warning C4309: 'initializing' : truncation
of constant value
lib\target\x86\X86InstrInfo.h(463) : warning C4341: 'VEX_L' : signed value is
out of range for enum constant
lib\target\x86\X86InstrInfo.h(463) : warning C4309: 'initializing' : truncation
of constant value

This is because of the following enum constants in the X86II namespace:

    // VEX - The opcode prefix used by AVX instructions
    VEX         = 1ULL << 32,

    // VEX_W - Has a opcode specific functionality, but is used in the same
    // way as REX_W is for regular SSE instructions.
    VEX_W       = 1ULL << 33,

    // VEX_4V - Used to specify an additional AVX/SSE register. Several 2
    // address instructions in SSE are represented as 3 address ones in AVX
    // and the additional register is encoded in VEX_VVVV prefix.
    VEX_4V      = 1ULL << 34,

    // VEX_I8IMM - Specifies that the last register used in a AVX instruction,
    // must be encoded in the i8 immediate field. This usually happens in
    // instructions with 4 operands.
    VEX_I8IMM   = 1ULL << 35,

    // VEX_L - Stands for a bit in the VEX opcode prefix meaning the current
    // instruction uses 256-bit wide registers. This is usually auto detected
if
    // a VR256 register is used, but some AVX instructions also have this field
    // marked when using a f256 memory references.
    VEX_L       = 1ULL << 36

So unfortunately VC++ truncates these constants, which is probably very
bad if you count on those exact values.  The MSDN library says the
following about this warning:

"An enumerated constant exceeds the limit for an int. The value of the
invalid constant is undefined. Constants must resolve to integers
between –4,294,967,295 and +4,294,967,295 (signed)."

http://msdn.microsoft.com/en-us/library/x651y302.aspx

Therefore, these constants should probably be replaced by globals, or
maybe even #defines... (yuck :)

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