David Greene
2008-Sep-26 15:38 UTC
[LLVMdev] Determining the register type of a MachineOperand
On Wednesday 24 September 2008 15:23, Mon Ping Wang wrote:> To my knowledge, I don't think there is an easy way to get the MVT > information from a MachineOperand. Why do you need it for? In mySee the thread I started on this very topic. Spilling is one place you'd like to have this information.> mind, the MachineInstr and its associated operands represent a > physical machine instruction and I typically want to think of those as > machine opcodes and machine register files. I am typically interested > in the mapping of MVTs to register classes when I'm generating machine > instructions. Note that a register class may map to multiple MVTs > depending on your description.Right, but the instruction opcode should give a clue about what the bits represent. That mapping is what's currently missing. -Dave
Villmow, Micah
2008-Sep-26 15:59 UTC
[LLVMdev] Determining the register type of a MachineOperand
Yes, Another reason this is useful is for register-type specific representations of said register. For example, all my registers are 128bit vector registers, however, if I am only dealing with 32 bit vector registers, I can add write/read masks that tell the underlying hardware not to work on the whole register, but just a subset of the components. 32bit scalar mov: mov r1.x___, r0.x000 64bit scalar mov: mov r1.xy__, r0.xy00 96bit scalar mov: mov r1.xyz_, r0.xyz0 128bit scalar mov: mov r1, r0 If I had the register type information at code generation time, then I can use the exact same tablegen pattern for all my register types and would only need to add the write/read masks in the printer instead of multiple patterns. Multiply this by over 100 opcodes and I save A LOT of work. -----Original Message----- From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of David Greene Sent: Friday, September 26, 2008 8:39 AM To: llvmdev at cs.uiuc.edu Subject: Re: [LLVMdev] Determining the register type of a MachineOperand On Wednesday 24 September 2008 15:23, Mon Ping Wang wrote:> To my knowledge, I don't think there is an easy way to get the MVT > information from a MachineOperand. Why do you need it for? In mySee the thread I started on this very topic. Spilling is one place you'd like to have this information.> mind, the MachineInstr and its associated operands represent a > physical machine instruction and I typically want to think of those as > machine opcodes and machine register files. I am typically interested > in the mapping of MVTs to register classes when I'm generating machine > instructions. Note that a register class may map to multiple MVTs > depending on your description.Right, but the instruction opcode should give a clue about what the bits represent. That mapping is what's currently missing. -Dave _______________________________________________ LLVM Developers mailing list LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
Evan Cheng
2008-Sep-29 16:01 UTC
[LLVMdev] Determining the register type of a MachineOperand
Sounds like you should specify a few class of pseudo registers mapped to the same set of registers. This is something we are considering for x86. That is, have xmm0_64, xmm0_32, and xmm0 all mapping to xmm0. If the first one is used, it means only the lower 64-bits are needed. An alternative is to encode such information in the opcode or as a pseudo immediate operand. Or, in the worst case, you can just iterate through all the uses / defs to determine the type Type information just doesn't belong on MachineOperand's. They belong to machine instructions, i.e. how they are defined / used. Evan On Sep 26, 2008, at 8:59 AM, Villmow, Micah wrote:> Yes, > Another reason this is useful is for register-type specific > representations of said register. > > For example, all my registers are 128bit vector registers, however, > if I > am only dealing with 32 bit vector registers, I can add write/read > masks > that tell the underlying hardware not to work on the whole register, > but > just a subset of the components. > 32bit scalar mov: mov r1.x___, r0.x000 > 64bit scalar mov: mov r1.xy__, r0.xy00 > 96bit scalar mov: mov r1.xyz_, r0.xyz0 > 128bit scalar mov: mov r1, r0 > > If I had the register type information at code generation time, then I > can use the exact same tablegen pattern for all my register types and > would only need to add the write/read masks in the printer instead of > multiple patterns. > > Multiply this by over 100 opcodes and I save A LOT of work. > > -----Original Message----- > From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] > On Behalf Of David Greene > Sent: Friday, September 26, 2008 8:39 AM > To: llvmdev at cs.uiuc.edu > Subject: Re: [LLVMdev] Determining the register type of a > MachineOperand > > On Wednesday 24 September 2008 15:23, Mon Ping Wang wrote: >> To my knowledge, I don't think there is an easy way to get the MVT >> information from a MachineOperand. Why do you need it for? In my > > See the thread I started on this very topic. Spilling is one place > you'd like > to have this information. > >> mind, the MachineInstr and its associated operands represent a >> physical machine instruction and I typically want to think of those >> as >> machine opcodes and machine register files. I am typically >> interested >> in the mapping of MVTs to register classes when I'm generating >> machine >> instructions. Note that a register class may map to multiple MVTs >> depending on your description. > > Right, but the instruction opcode should give a clue about what the > bits > > represent. That mapping is what's currently missing. > > -Dave > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev > > > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
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