[Docs][CodeGenerator] Don't specify the number of operands in BuildMI

[thegameg]

Summary

Since rL31947, MI constructors take a TargetInstrDescriptor, instead of an instruction and a number of operands. The documentation seems to be outdated.

[kparzysz]

docs/CodeGenerator.rst

391 ↗

(On Diff #62144)

Typo.

392 ↗

(On Diff #62144)

The "get" function is in TargetInstrInfo. Could you make it explicit in the examples? E.g.

MachineInstr *MI = BuildMI(MBB, DL, TII.get(X86::MOV32ri), DestReg).addImm(42);

[thegameg]

DebufLoc -> DebugLog. My bad.

Use TTI.get(Opcode) instead of get(Opcode).

[kparzysz]

docs/CodeGenerator.rst

390 ↗

(On Diff #62219)

In the LLVM sources, TTI usually denotes TargetTransformInfo. A reference to TargetInstrInfo is usually held in TII.

[thegameg]

TTI -> TII.

Thank you for your patience :/.

[thegameg]

Thanks kparzysz. I don't have commit access, can you commit this for me, please? Thanks.

llvm/trunk/docs/CodeGenerator.rst

 Machine instructions are created by using the ``BuildMI`` functions, located in
 the ``include/llvm/CodeGen/MachineInstrBuilder.h`` file.  The ``BuildMI``
 functions make it easy to build arbitrary machine instructions.  Usage of the
 ``BuildMI`` functions look like this:
 
 .. code-block:: c++
 
   // Create a 'DestReg = mov 42' (rendered in X86 assembly as 'mov DestReg, 42')
-  // instruction.  The '1' specifies how many operands will be added.
-  MachineInstr *MI = BuildMI(X86::MOV32ri, 1, DestReg).addImm(42);
-
-  // Create the same instr, but insert it at the end of a basic block.
+  // instruction and insert it at the end of the given MachineBasicBlock.
+  const TargetInstrInfo &TII = ...
   MachineBasicBlock &MBB = ...
-  BuildMI(MBB, X86::MOV32ri, 1, DestReg).addImm(42);
+  DebugLoc DL;
+  MachineInstr *MI = BuildMI(MBB, DL, TII.get(X86::MOV32ri), DestReg).addImm(42);
 
   // Create the same instr, but insert it before a specified iterator point.
   MachineBasicBlock::iterator MBBI = ...
-  BuildMI(MBB, MBBI, X86::MOV32ri, 1, DestReg).addImm(42);
+  BuildMI(MBB, MBBI, DL, TII.get(X86::MOV32ri), DestReg).addImm(42);
 
   // Create a 'cmp Reg, 0' instruction, no destination reg.
-  MI = BuildMI(X86::CMP32ri, 2).addReg(Reg).addImm(0);
+  MI = BuildMI(MBB, DL, TII.get(X86::CMP32ri8)).addReg(Reg).addImm(42);
 
   // Create an 'sahf' instruction which takes no operands and stores nothing.
-  MI = BuildMI(X86::SAHF, 0);
+  MI = BuildMI(MBB, DL, TII.get(X86::SAHF));
 
   // Create a self looping branch instruction.
-  BuildMI(MBB, X86::JNE, 1).addMBB(&MBB);
+  BuildMI(MBB, DL, TII.get(X86::JNE)).addMBB(&MBB);
 
-The key thing to remember with the ``BuildMI`` functions is that you have to
-specify the number of operands that the machine instruction will take.  This
-allows for efficient memory allocation.  You also need to specify if operands
-default to be uses of values, not definitions.  If you need to add a definition
-operand (other than the optional destination register), you must explicitly mark
-it as such:
+If you need to add a definition operand (other than the optional destination
+register), you must explicitly mark it as such:
 
 .. code-block:: c++
 
   MI.addReg(Reg, RegState::Define);
 
 Fixed (preassigned) registers
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

llvm/trunk/include/llvm/CodeGen/MachineInstrBuilder.h

 //===-- CodeGen/MachineInstBuilder.h - Simplify creation of MIs -*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file exposes a function named BuildMI, which is useful for dramatically
 // simplifying how MachineInstr's are created.  It allows use of code like this:
 //
-//   M = BuildMI(X86::ADDrr8, 2).addReg(argVal1).addReg(argVal2);
+//   M = BuildMI(MBB, MI, DL, TII.get(X86::ADD8rr), Dst)
+//           .addReg(argVal1)
+//           .addReg(argVal2);
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CODEGEN_MACHINEINSTRBUILDER_H
 #define LLVM_CODEGEN_MACHINEINSTRBUILDER_H
 
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineInstrBundle.h"