[RISCV] Custom lower llvm.clear_cache on glibc targets

Typically __clear_cache is used but on these targets __riscv_flush_icache
is used instead. Because it also has a different signature we need
custom lowering.

Author: rofirrim

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -662,6 +662,11 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
 
   setBooleanContents(ZeroOrOneBooleanContent);
 
+  if (Subtarget.getTargetTriple().isOSGlibc()) {
+    // Custom lowering of llvm.clear_cache.
+    setOperationAction(ISD::CLEAR_CACHE, MVT::Other, Custom);
+  }
+
   if (Subtarget.hasVInstructions()) {
     setBooleanVectorContents(ZeroOrOneBooleanContent);
 
@@ -7152,7 +7157,48 @@ SDValue RISCVTargetLowering::LowerOperation(SDValue Op,
     return lowerVPSpliceExperimental(Op, DAG);
   case ISD::EXPERIMENTAL_VP_REVERSE:
     return lowerVPReverseExperimental(Op, DAG);
+  case ISD::CLEAR_CACHE: {
+    assert(Subtarget.getTargetTriple().isOSGlibc() &&
+           "llvm.clear_cache only needs custom lower on glibc targets");
+    SDLoc DL(Op);
+    SDValue Flags = DAG.getConstant(0, DL, Subtarget.getXLenVT());
+    return emitFlushICache(DAG, Op.getOperand(0), Op.getOperand(1),
+                           Op.getOperand(2), Flags, DL);
   }
+  }
+}
+
+SDValue RISCVTargetLowering::emitFlushICache(SelectionDAG &DAG, SDValue InChain,
+                                             SDValue Start, SDValue End,
+                                             SDValue Flags, SDLoc DL) const {
+  TargetLowering::ArgListTy Args;
+  TargetLowering::ArgListEntry Entry;
+
+  // start
+  Entry.Node = Start;
+  Entry.Ty = PointerType::getUnqual(*DAG.getContext());
+  Args.push_back(Entry);
+
+  // end
+  Entry.Node = End;
+  Entry.Ty = PointerType::getUnqual(*DAG.getContext());
+  Args.push_back(Entry);
+
+  // flags
+  Entry.Node = Flags;
+  Entry.Ty = Type::getIntNTy(*DAG.getContext(), Subtarget.getXLen());
+  Args.push_back(Entry);
+
+  TargetLowering::CallLoweringInfo CLI(DAG);
+  EVT Ty = getPointerTy(DAG.getDataLayout());
+  CLI.setDebugLoc(DL).setChain(InChain).setLibCallee(
+      CallingConv::C, Type::getVoidTy(*DAG.getContext()),
+      DAG.getExternalSymbol("__riscv_flush_icache", Ty), std::move(Args));
+
+  std::pair<SDValue, SDValue> CallResult = LowerCallTo(CLI);
+
+  // This function returns void so only the out chain matters.
+  return CallResult.second;
 }
 
 static SDValue getTargetNode(GlobalAddressSDNode *N, const SDLoc &DL, EVT Ty,

llvm/lib/Target/RISCV/RISCVISelLowering.h

@@ -1037,6 +1037,9 @@ class RISCVTargetLowering : public TargetLowering {
                                          const APInt &AndMask) const override;
 
   unsigned getMinimumJumpTableEntries() const override;
+
+  SDValue emitFlushICache(SelectionDAG &DAG, SDValue InChain, SDValue Start,
+                          SDValue End, SDValue Flags, SDLoc DL) const;
 };
 
 /// As per the spec, the rules for passing vector arguments are as follows:

llvm/test/CodeGen/RISCV/clear-cache.ll

@@ -0,0 +1,49 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=riscv32 < %s | FileCheck --check-prefix=RV32 %s
+; RUN: llc -mtriple=riscv64 < %s | FileCheck --check-prefix=RV64 %s
+; RUN: llc -mtriple=riscv32-unknown-linux-gnu < %s | FileCheck --check-prefix=RV32-GLIBC %s
+; RUN: llc -mtriple=riscv64-unknown-linux-gnu < %s | FileCheck --check-prefix=RV64-GLIBC %s
+
+declare void @llvm.clear_cache(ptr, ptr)
+
+define void @foo(ptr %a, ptr %b) nounwind {
+; RV32-LABEL: foo:
+; RV32:       # %bb.0:
+; RV32-NEXT:    addi sp, sp, -16
+; RV32-NEXT:    sw ra, 12(sp) # 4-byte Folded Spill
+; RV32-NEXT:    call __clear_cache
+; RV32-NEXT:    lw ra, 12(sp) # 4-byte Folded Reload
+; RV32-NEXT:    addi sp, sp, 16
+; RV32-NEXT:    ret
+;
+; RV64-LABEL: foo:
+; RV64:       # %bb.0:
+; RV64-NEXT:    addi sp, sp, -16
+; RV64-NEXT:    sd ra, 8(sp) # 8-byte Folded Spill
+; RV64-NEXT:    call __clear_cache
+; RV64-NEXT:    ld ra, 8(sp) # 8-byte Folded Reload
+; RV64-NEXT:    addi sp, sp, 16
+; RV64-NEXT:    ret
+;
+; RV32-GLIBC-LABEL: foo:
+; RV32-GLIBC:       # %bb.0:
+; RV32-GLIBC-NEXT:    addi sp, sp, -16
+; RV32-GLIBC-NEXT:    sw ra, 12(sp) # 4-byte Folded Spill
+; RV32-GLIBC-NEXT:    li a2, 0
+; RV32-GLIBC-NEXT:    call __riscv_flush_icache
+; RV32-GLIBC-NEXT:    lw ra, 12(sp) # 4-byte Folded Reload
+; RV32-GLIBC-NEXT:    addi sp, sp, 16
+; RV32-GLIBC-NEXT:    ret
+;
+; RV64-GLIBC-LABEL: foo:
+; RV64-GLIBC:       # %bb.0:
+; RV64-GLIBC-NEXT:    addi sp, sp, -16
+; RV64-GLIBC-NEXT:    sd ra, 8(sp) # 8-byte Folded Spill
+; RV64-GLIBC-NEXT:    li a2, 0
+; RV64-GLIBC-NEXT:    call __riscv_flush_icache
+; RV64-GLIBC-NEXT:    ld ra, 8(sp) # 8-byte Folded Reload
+; RV64-GLIBC-NEXT:    addi sp, sp, 16
+; RV64-GLIBC-NEXT:    ret
+  call void @llvm.clear_cache(ptr %a, ptr %b)
+  ret void
+}