FDIV/FLDCW Instructions

fdiv/fldcw_Stall indicates a penalty condition.

The floating-point instruction for which fdiv/fldcw_Stall is issued cannot begin executing until the previous FDIV or FLDCW instruction finishes executing its latency clocks. No other floating-point instruction can execute while FDIV or FLDCW executes.

Tip

Follow these guidelines to prevent the penalty condition:

• Organize your code so that integer instructions execute while the FLDCW or FDIV instruction executes its latency clocks.

• Schedule other floating-point instructions for execution only after the FLDCW or FDIV instruction finishes executing.

Example:

1. fdiv DWORD PTR [ebp-4]
2. fadd st(0), st(1)
3. mov eax, 1
4. mov ebx, 1
5. mov ecx, 1

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1. fdiv DWORD PTR [ebp-4]
3. mov eax, 1
4. mov ebx, 1
5. mov ecx, 1
2. fadd st(0), st(1)

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2
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39