diff --git a/llvm/lib/Target/RISCV/RISCVFrameLowering.h b/llvm/lib/Target/RISCV/RISCVFrameLowering.h --- a/llvm/lib/Target/RISCV/RISCVFrameLowering.h +++ b/llvm/lib/Target/RISCV/RISCVFrameLowering.h @@ -59,6 +59,9 @@ // epilogue. uint64_t getFirstSPAdjustAmount(const MachineFunction &MF) const; + bool canUseAsPrologue(const MachineBasicBlock &MBB) const override; + bool canUseAsEpilogue(const MachineBasicBlock &MBB) const override; + protected: const RISCVSubtarget &STI; diff --git a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp b/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp --- a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp +++ b/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp @@ -747,3 +747,47 @@ return true; } + +bool RISCVFrameLowering::canUseAsPrologue(const MachineBasicBlock &MBB) const { + MachineBasicBlock *TmpMBB = const_cast(&MBB); + const auto *RVFI = MBB.getParent()->getInfo(); + + if (!RVFI->useSaveRestoreLibCalls()) + return true; + + // Inserting a call to a __riscv_save libcall requires the use of the register + // t0 (X5) to hold the return address. Therefore if this register is already + // used we can't insert the call. + + RegScavenger RS; + RS.enterBasicBlock(*TmpMBB); + return !RS.isRegUsed(RISCV::X5); +} + +bool RISCVFrameLowering::canUseAsEpilogue(const MachineBasicBlock &MBB) const { + MachineBasicBlock *TmpMBB = const_cast(&MBB); + const auto *RVFI = MBB.getParent()->getInfo(); + + if (!RVFI->useSaveRestoreLibCalls()) + return true; + + // Using the __riscv_restore libcalls to restore CSRs requires a tail call. + // This means if we still need to continue executing code within this function + // the restore cannot take place in this basic block. + + if (MBB.succ_size() > 1) + return false; + + MachineBasicBlock *SuccMBB = + MBB.succ_empty() ? TmpMBB->getFallThrough() : *MBB.succ_begin(); + + // Doing a tail call should be safe if there are no successors, because either + // we have a returning block or the end of the block is unreachable, so the + // restore will be eliminated regardless. + if (!SuccMBB) + return true; + + // The successor can only contain a return, since we would effectively be + // replacing the successor with our own tail return at the end of our block. + return SuccMBB->isReturnBlock() && SuccMBB->size() == 1; +} diff --git a/llvm/test/CodeGen/RISCV/shrinkwrap.ll b/llvm/test/CodeGen/RISCV/shrinkwrap.ll --- a/llvm/test/CodeGen/RISCV/shrinkwrap.ll +++ b/llvm/test/CodeGen/RISCV/shrinkwrap.ll @@ -1,6 +1,8 @@ ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py ; RUN: llc -mtriple riscv32 < %s | FileCheck %s -check-prefix=RV32I-NOSW ; RUN: llc -mtriple riscv32 -enable-shrink-wrap < %s | FileCheck %s -check-prefix=RV32I-SW +; RUN: llc -mtriple riscv32 -enable-shrink-wrap -mattr=+save-restore < %s \ +; RUN: | FileCheck %s -check-prefix=RV32I-SW-SR declare void @abort() @@ -29,6 +31,16 @@ ; RV32I-SW-NEXT: addi sp, sp, -16 ; RV32I-SW-NEXT: sw ra, 12(sp) ; RV32I-SW-NEXT: call abort +; +; RV32I-SW-SR-LABEL: eliminate_restore: +; RV32I-SW-SR: # %bb.0: +; RV32I-SW-SR-NEXT: addi a1, zero, 32 +; RV32I-SW-SR-NEXT: bgeu a1, a0, .LBB0_2 +; RV32I-SW-SR-NEXT: # %bb.1: # %if.end +; RV32I-SW-SR-NEXT: ret +; RV32I-SW-SR-NEXT: .LBB0_2: # %if.then +; RV32I-SW-SR-NEXT: call t0, __riscv_save_0 +; RV32I-SW-SR-NEXT: call abort %cmp = icmp ule i32 %n, 32 br i1 %cmp, label %if.then, label %if.end @@ -84,6 +96,23 @@ ; RV32I-SW-NEXT: addi sp, sp, 16 ; RV32I-SW-NEXT: .LBB1_2: # %if.end ; RV32I-SW-NEXT: ret +; +; RV32I-SW-SR-LABEL: conditional_alloca: +; RV32I-SW-SR: # %bb.0: +; RV32I-SW-SR-NEXT: addi a1, zero, 32 +; RV32I-SW-SR-NEXT: bltu a1, a0, .LBB1_2 +; RV32I-SW-SR-NEXT: # %bb.1: # %if.then +; RV32I-SW-SR-NEXT: call t0, __riscv_save_1 +; RV32I-SW-SR-NEXT: addi s0, sp, 16 +; RV32I-SW-SR-NEXT: addi a0, a0, 15 +; RV32I-SW-SR-NEXT: andi a0, a0, -16 +; RV32I-SW-SR-NEXT: sub a0, sp, a0 +; RV32I-SW-SR-NEXT: mv sp, a0 +; RV32I-SW-SR-NEXT: call notdead +; RV32I-SW-SR-NEXT: addi sp, s0, -16 +; RV32I-SW-SR-NEXT: tail __riscv_restore_1 +; RV32I-SW-SR-NEXT: .LBB1_2: # %if.end +; RV32I-SW-SR-NEXT: ret %cmp = icmp ule i32 %n, 32 br i1 %cmp, label %if.then, label %if.end