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Add information about memory index representation

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@4712 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2002-11-17 20:33:26 +00:00
parent e7236ffa94
commit 1411ba31ba
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lib/Target/X86/README.txt
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@ -128,8 +128,33 @@ This directory contains regression tests for the JIT. Initially it contains a
bunch of really trivial testcases that we should build up to supporting.
===================================================
IV. Strange Things, or, Things That Should Be Known
===================================================
Representing memory in MachineInstrs
------------------------------------
The x86 has a very, uhm, flexible, way of accessing memory. It is capable of
addressing memory addresses of the following form directly in integer
instructions (which use ModR/M addressing):
Base+[1,2,4,8]*IndexReg+Disp32
Wow, that's crazy. In order to represent this, LLVM tracks no less that 4
operands for each memory operand of this form. This means that the "load" form
of 'mov' has the following "Operands" in this order:
Index: 0 | 1 2 3 4
Meaning: DestReg, | BaseReg, Scale, IndexReg, Displacement
OperandTy: VirtReg, | VirtReg, UnsImm, VirtReg, SignExtImm
Stores and all other instructions treat the four memory operands in the same
way, in the same order.
==========================
IV. TODO / Future Projects
V. TODO / Future Projects
==========================
There are a large number of things remaining to do. Here is a partial list: