[llvm-commits] [llvm] r59876 - /llvm/trunk/docs/WritingAnLLVMBackend.html
Chris Lattner
sabre at nondot.org
Sat Nov 22 11:10:48 PST 2008
Author: lattner
Date: Sat Nov 22 13:10:48 2008
New Revision: 59876
URL: http://llvm.org/viewvc/llvm-project?rev=59876&view=rev
Log:
Describe how the JIT maps fields to MachineOperands, patch by
JP Bonn!
Modified:
llvm/trunk/docs/WritingAnLLVMBackend.html
Modified: llvm/trunk/docs/WritingAnLLVMBackend.html
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/WritingAnLLVMBackend.html?rev=59876&r1=59875&r2=59876&view=diff
==============================================================================
--- llvm/trunk/docs/WritingAnLLVMBackend.html (original)
+++ llvm/trunk/docs/WritingAnLLVMBackend.html Sat Nov 22 13:10:48 2008
@@ -29,6 +29,7 @@
</ul></li>
<li><a href="#InstructionSet">Instruction Set</a>
<ul>
+ <li><a href="#operandMapping">Instruction Operand Mapping</a></li>
<li><a href="#implementInstr">Implement a subclass of TargetInstrInfo</a></li>
<li><a href="#branchFolding">Branch Folding and If Conversion</a></li>
</ul></li>
@@ -998,6 +999,88 @@
<!-- ======================================================================= -->
<div class="doc_subsection">
+ <a name="operandMapping">Instruction Operand Mapping</a>
+</div>
+<div class="doc_text">
+<p>The code generator backend maps instruction operands to fields in
+the instruction. Operands are assigned to unbound fields in the instruction in
+the order they are defined. Fields are bound when they are assigned a value.
+For example, the Sparc target defines the XNORrr instruction as a F3_1 format
+instruction having three operands.</p>
+</div>
+
+<div class="doc_code"> <pre>
+def XNORrr : F3_1<2, 0b000111,
+ (outs IntRegs:$dst), (ins IntRegs:$b, IntRegs:$c),
+ "xnor $b, $c, $dst",
+ [(set IntRegs:$dst, (not (xor IntRegs:$b, IntRegs:$c)))]>;
+</pre></div>
+
+<div class="doc_text">
+<p>The instruction templates in <tt>SparcInstrFormats.td</tt> show the base class for F3_1 is InstSP.</p>
+</div>
+
+<div class="doc_code"> <pre>
+class InstSP<dag outs, dag ins, string asmstr, list<dag> pattern> : Instruction {
+ field bits<32> Inst;
+ let Namespace = "SP";
+ bits<2> op;
+ let Inst{31-30} = op;
+ dag OutOperandList = outs;
+ dag InOperandList = ins;
+ let AsmString = asmstr;
+ let Pattern = pattern;
+}
+</pre></div>
+<div class="doc_text">
+<p>
+InstSP leaves the op field unbound.
+</p>
+</div>
+
+<div class="doc_code"> <pre>
+class F3<dag outs, dag ins, string asmstr, list<dag> pattern>
+ : InstSP<outs, ins, asmstr, pattern> {
+ bits<5> rd;
+ bits<6> op3;
+ bits<5> rs1;
+ let op{1} = 1; // Op = 2 or 3
+ let Inst{29-25} = rd;
+ let Inst{24-19} = op3;
+ let Inst{18-14} = rs1;
+}
+</pre></div>
+<div class="doc_text">
+<p>
+F3 binds the op field and defines the rd, op3, and rs1 fields. F3 format instructions will
+bind the operands rd, op3, and rs1 fields.
+</p>
+</div>
+
+<div class="doc_code"> <pre>
+class F3_1<bits<2> opVal, bits<6> op3val, dag outs, dag ins,
+ string asmstr, list<dag> pattern> : F3<outs, ins, asmstr, pattern> {
+ bits<8> asi = 0; // asi not currently used
+ bits<5> rs2;
+ let op = opVal;
+ let op3 = op3val;
+ let Inst{13} = 0; // i field = 0
+ let Inst{12-5} = asi; // address space identifier
+ let Inst{4-0} = rs2;
+}
+</pre></div>
+<div class="doc_text">
+<p>
+F3_1 binds the op3 field and defines the rs2 fields. F3_1 format instructions will
+bind the operands to the rd, rs1, and rs2 fields. This results in the XNORrr instruction
+binding $dst, $b, and $c operands to the rd, rs1, and rs2 fields respectively.
+</p>
+</div>
+
+
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
<a name="implementInstr">Implement a subclass of </a>
<a href="http://www.llvm.org/docs/CodeGenerator.html#targetinstrinfo">TargetInstrInfo</a>
</div>
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