Index: llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp =================================================================== --- llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp +++ llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp @@ -379,9 +379,14 @@ const TargetRegisterClass *RC = MRI.getRegClass(OldReg); Register NewReg = MRI.createVirtualRegister(RC); unsigned Opc = getLocalGetOpcode(RC); - InsertPt = - BuildMI(MBB, InsertPt, MI.getDebugLoc(), TII->get(Opc), NewReg) - .addImm(LocalId); + // Use a InsertPt as our DebugLoc, since MI may be discontinuous from + // the where this local is being inserted, causing non-linear stepping + // in the debugger or function entry points where variables aren't live + // yet. Alternative is previous instruction, but that is strictly worse + // since it can point at the previous statement. + // See crbug.com/1251909, crbug.com/1249745 + InsertPt = BuildMI(MBB, InsertPt, InsertPt->getDebugLoc(), + TII->get(Opc), NewReg).addImm(LocalId); MO.setReg(NewReg); MFI.stackifyVReg(MRI, NewReg); Changed = true;