From 633c24464c84612bd7736b5f4ff7bbf2d3a25bfc Mon Sep 17 00:00:00 2001 From: Matt Arsenault Date: Fri, 3 Oct 2025 14:42:32 +0900 Subject: [PATCH 1/2] AMDGPU: Remove dead code trying to constrain a physical register This constrainRegClass check would never pass for a physical register. --- llvm/lib/Target/AMDGPU/SIInstrInfo.cpp | 23 ++++++++--------------- 1 file changed, 8 insertions(+), 15 deletions(-) diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp index 56435a50c87ad..fe6b8b96cbd57 100644 --- a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp +++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp @@ -8117,21 +8117,14 @@ void SIInstrInfo::moveToVALUImpl(SIInstrWorklist &Worklist, // hope for the best. if (Inst.isCopy() && DstReg.isPhysical() && RI.isVGPR(MRI, Inst.getOperand(1).getReg())) { - // TODO: Only works for 32 bit registers. - if (MRI.constrainRegClass(DstReg, &AMDGPU::SReg_32_XM0RegClass)) { - BuildMI(*Inst.getParent(), &Inst, Inst.getDebugLoc(), - get(AMDGPU::V_READFIRSTLANE_B32), DstReg) - .add(Inst.getOperand(1)); - } else { - Register NewDst = - MRI.createVirtualRegister(&AMDGPU::SReg_32_XM0RegClass); - BuildMI(*Inst.getParent(), &Inst, Inst.getDebugLoc(), - get(AMDGPU::V_READFIRSTLANE_B32), NewDst) - .add(Inst.getOperand(1)); - BuildMI(*Inst.getParent(), &Inst, Inst.getDebugLoc(), get(AMDGPU::COPY), - DstReg) - .addReg(NewDst); - } + Register NewDst = MRI.createVirtualRegister(&AMDGPU::SReg_32_XM0RegClass); + BuildMI(*Inst.getParent(), &Inst, Inst.getDebugLoc(), + get(AMDGPU::V_READFIRSTLANE_B32), NewDst) + .add(Inst.getOperand(1)); + BuildMI(*Inst.getParent(), &Inst, Inst.getDebugLoc(), get(AMDGPU::COPY), + DstReg) + .addReg(NewDst); + Inst.eraseFromParent(); return; } From cf04ae0c7c664d2fba2995eae7ce825fa4badd95 Mon Sep 17 00:00:00 2001 From: Matt Arsenault Date: Fri, 3 Oct 2025 14:29:14 +0900 Subject: [PATCH 2/2] AMDGPU: Stop trying to constrain register class of post-RA-pseudos This is trying to constrain the register class of a physical register, which makes no sense. --- llvm/lib/Target/AMDGPU/SIInstrInfo.cpp | 2 -- 1 file changed, 2 deletions(-) diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp index fe6b8b96cbd57..cda8069936af2 100644 --- a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp +++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp @@ -2112,8 +2112,6 @@ bool SIInstrInfo::expandPostRAPseudo(MachineInstr &MI) const { case AMDGPU::SI_RESTORE_S32_FROM_VGPR: MI.setDesc(get(AMDGPU::V_READLANE_B32)); - MI.getMF()->getRegInfo().constrainRegClass(MI.getOperand(0).getReg(), - &AMDGPU::SReg_32_XM0RegClass); break; case AMDGPU::AV_MOV_B32_IMM_PSEUDO: { Register Dst = MI.getOperand(0).getReg();