1 //===- AVRShift.cpp - Shift Expansion Pass --------------------------------===//
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
10 /// Expand non-8-bit and non-16-bit shift instructions (shl, lshr, ashr) to
11 /// inline loops, just like avr-gcc. This must be done in IR because otherwise
12 /// the type legalizer will turn 32-bit shifts into (non-existing) library calls
15 //===----------------------------------------------------------------------===//
33   StringRef getPassName() const override { return "AVR Shift Expansion"; }  in getPassName()
43 INITIALIZE_PASS(AVRShiftExpand, "avr-shift-expand", "AVR Shift Expansion",
53       // Only expand shift instructions (shl, lshr, ashr).  in runOnFunction()
56       // Only expand non-8-bit and non-16-bit shifts, since those are expanded  in runOnFunction()
60       // Only expand when the shift amount is not known.  in runOnFunction()
61       // Known shift amounts are (currently) better expanded inline.  in runOnFunction()
73   // Return whether this function expanded any shift instructions.  in runOnFunction()
78   auto &Ctx = BI->getContext();  in expand()
80   Type *InputTy = cast<Instruction>(BI)->getType();  in expand()
84   // Split the current basic block at the point of the existing shift  in expand()
86   BasicBlock *BB = BI->getParent();  in expand()
87   Function *F = BB->getParent();  in expand()
88   BasicBlock *EndBB = BB->splitBasicBlock(BI, "shift.done");  in expand()
89   BasicBlock *LoopBB = BasicBlock::Create(Ctx, "shift.loop", F, EndBB);  in expand()
91   // Truncate the shift amount to i8, which is trivially lowered to a single  in expand()
93   Builder.SetInsertPoint(&BB->back());  in expand()
94   Value *ShiftAmount = Builder.CreateTrunc(BI->getOperand(1), Int8Ty);  in expand()
100   BB->back().eraseFromParent();  in expand()
105   ShiftAmountPHI->addIncoming(ShiftAmount, BB);  in expand()
107   ValuePHI->addIncoming(BI->getOperand(0), BB);  in expand()
109   // Subtract the shift amount by one, as we're shifting one this loop  in expand()
113   ShiftAmountPHI->addIncoming(ShiftAmountSub, LoopBB);  in expand()
115   // Emit the actual shift instruction. The difference is that this shift  in expand()
116   // instruction has a constant shift amount, which can be emitted inline  in expand()
119   switch (BI->getOpcode()) {  in expand()
130     llvm_unreachable("asked to expand an instruction that is not a shift");  in expand()
132   ValuePHI->addIncoming(ValueShifted, LoopBB);  in expand()
134   // Branch to either the loop again (if there is more to shift) or to the  in expand()
143   Result->addIncoming(BI->getOperand(0), BB);  in expand()
144   Result->addIncoming(ValueShifted, LoopBB);  in expand()
146   // Replace the original shift instruction.  in expand()
147   BI->replaceAllUsesWith(Result);  in expand()
148   BI->eraseFromParent();  in expand()