[PowerPC] Implement fence builtin (#76495)

Author: ecnelises

clang/include/clang/Basic/BuiltinsPPC.def

@@ -110,6 +110,10 @@ BUILTIN(__builtin_ppc_fctiw, "dd", "")
 BUILTIN(__builtin_ppc_fctiwz, "dd", "")
 BUILTIN(__builtin_ppc_fctudz, "dd", "")
 BUILTIN(__builtin_ppc_fctuwz, "dd", "")
+
+// fence builtin prevents all instructions moved across it
+BUILTIN(__builtin_ppc_fence, "v", "")
+
 BUILTIN(__builtin_ppc_swdiv_nochk, "ddd", "")
 BUILTIN(__builtin_ppc_swdivs_nochk, "fff", "")
 BUILTIN(__builtin_ppc_alignx, "vIivC*", "nc")

clang/lib/Basic/Targets/PPC.cpp

@@ -212,6 +212,7 @@ static void defineXLCompatMacros(MacroBuilder &Builder) {
   Builder.defineMacro("__darn_32", "__builtin_darn_32");
   Builder.defineMacro("__darn_raw", "__builtin_darn_raw");
   Builder.defineMacro("__dcbf", "__builtin_dcbf");
+  Builder.defineMacro("__fence", "__builtin_ppc_fence");
   Builder.defineMacro("__fmadd", "__builtin_fma");
   Builder.defineMacro("__fmadds", "__builtin_fmaf");
   Builder.defineMacro("__abs", "__builtin_abs");

clang/test/CodeGen/PowerPC/builtins-ppc-xlcompat-sync.c

@@ -194,6 +194,18 @@ void test_dcbz() {
   __dcbz(c);
 }
 
+// CHECK-LABEL: @test_fence(
+// CHECK:         call void @llvm.ppc.fence()
+// CHECK-NEXT:    ret void
+//
+// CHECK-32-LABEL: @test_fence(
+// CHECK-32:         call void @llvm.ppc.fence()
+// CHECK-32-NEXT:    ret void
+//
+void test_fence() {
+  __fence();
+}
+
 // CHECK-LABEL: @test_builtin_ppc_popcntb(
 // CHECK:    [[TMP0:%.*]] = load i64, ptr @a, align 8
 // CHECK-NEXT:    [[POPCNTB:%.*]] = call i64 @llvm.ppc.popcntb.i64.i64(i64 [[TMP0]])
@@ -375,3 +387,15 @@ void test_builtin_ppc_dcbtst() {
 void test_builtin_ppc_dcbz() {
   __builtin_ppc_dcbz(c);
 }
+
+// CHECK-LABEL: @test_builtin_ppc_fence(
+// CHECK:         call void @llvm.ppc.fence()
+// CHECK-NEXT:    ret void
+//
+// CHECK-32-LABEL: @test_builtin_ppc_fence(
+// CHECK-32:         call void @llvm.ppc.fence()
+// CHECK-32-NEXT:    ret void
+//
+void test_builtin_ppc_fence() {
+  __builtin_ppc_fence();
+}

llvm/include/llvm/IR/IntrinsicsPowerPC.td

@@ -29,6 +29,11 @@ let TargetPrefix = "ppc" in {  // All intrinsics start with "llvm.ppc.".
     [IntrArgMemOnly, NoCapture<ArgIndex<0>>, ImmArg<ArgIndex<1>>]>;
   def int_ppc_dcbzl : Intrinsic<[], [llvm_ptr_ty], []>;
 
+  // Emit pseudo instruction as fence of instruction motion
+  def int_ppc_fence : ClangBuiltin<"__builtin_ppc_fence">,
+                      DefaultAttrsIntrinsic<[], [],
+                                            [IntrNoMerge, IntrHasSideEffects]>;
+
   // Get content from current FPSCR register
   def int_ppc_readflm : ClangBuiltin<"__builtin_readflm">,
                         DefaultAttrsIntrinsic<[llvm_double_ty], [],

llvm/lib/Target/PowerPC/PPCInstrInfo.cpp

@@ -2155,11 +2155,17 @@ bool PPCInstrInfo::isPredicated(const MachineInstr &MI) const {
 bool PPCInstrInfo::isSchedulingBoundary(const MachineInstr &MI,
                                         const MachineBasicBlock *MBB,
                                         const MachineFunction &MF) const {
+  switch (MI.getOpcode()) {
+  default:
+    break;
   // Set MFFS and MTFSF as scheduling boundary to avoid unexpected code motion
   // across them, since some FP operations may change content of FPSCR.
   // TODO: Model FPSCR in PPC instruction definitions and remove the workaround
-  if (MI.getOpcode() == PPC::MFFS || MI.getOpcode() == PPC::MTFSF)
+  case PPC::MFFS:
+  case PPC::MTFSF:
+  case PPC::FENCE:
     return true;
+  }
   return TargetInstrInfo::isSchedulingBoundary(MI, MBB, MF);
 }
 

llvm/lib/Target/PowerPC/PPCInstrInfo.td

@@ -1328,6 +1328,9 @@ def SETFLM : PPCCustomInserterPseudo<(outs f8rc:$FRT), (ins f8rc:$FLM),
                     "#SETFLM", [(set f64:$FRT, (int_ppc_setflm f8rc:$FLM))]>;
 }
 
+let isBarrier = 1, hasSideEffects = 1, Defs = [RM] in
+def FENCE : PPCEmitTimePseudo<(outs), (ins), "#FENCE", []>;
+
 let Defs = [LR] in
   def MovePCtoLR : PPCEmitTimePseudo<(outs), (ins), "#MovePCtoLR", []>,
                    PPC970_Unit_BRU;
@@ -3187,6 +3190,7 @@ def : Pat<(PPCtc_return (i32 texternalsym:$dst), imm:$imm),
 def : Pat<(PPCtc_return CTRRC:$dst, imm:$imm),
           (TCRETURNri CTRRC:$dst, imm:$imm)>;
 
+def : Pat<(int_ppc_fence), (FENCE)>;
 def : Pat<(int_ppc_readflm), (MFFS)>;
 def : Pat<(int_ppc_mffsl), (MFFSL)>;
 

llvm/test/CodeGen/PowerPC/fence.ll

@@ -0,0 +1,45 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -verify-machineinstrs -mtriple=powerpc64-ibm-aix \
+; RUN:   -mcpu=pwr7 < %s | FileCheck %s
+; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-linux \
+; RUN:   -mcpu=pwr8 < %s | FileCheck %s
+; RUN: llc < %s -mtriple powerpc64le-unknown-linux -debug-only=machine-scheduler \
+; RUN:   2>&1 | FileCheck %s --check-prefix=LOG
+
+define dso_local void @test_builtin_ppc_fence() {
+; CHECK-LABEL: test_builtin_ppc_fence:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    #FENCE
+; CHECK-NEXT:    blr
+entry:
+  call void @llvm.ppc.fence()
+  ret void
+}
+declare void @llvm.ppc.fence()
+
+; LOG: ***** MI Scheduling *****
+; LOG-NEXT: motion:%bb.0 entry
+; LOG: ExitSU: FENCE implicit-def dead $rm
+; LOG: ***** MI Scheduling *****
+; LOG-NEXT: motion:%bb.0 entry
+; LOG: ExitSU: FENCE implicit-def dead $rm
+;
+; LOG: ***** MI Scheduling *****
+; LOG-NEXT: motion:%bb.0 entry
+; LOG: ExitSU: FENCE implicit-def dead $rm
+; LOG: ***** MI Scheduling *****
+; LOG-NEXT: motion:%bb.0 entry
+; LOG: ExitSU: FENCE implicit-def dead $rm
+define double @motion(double %a, double %b, double %c, double %d) {
+entry:
+  %0 = fdiv double %a, %b
+  %1 = fdiv double %b, %d
+  call void @llvm.ppc.fence()
+  %2 = fdiv double %c, %d
+  %3 = fdiv double %a, %c
+  call void @llvm.ppc.fence()
+  %4 = fadd double %0, %1
+  %5 = fadd double %2, %3
+  %6 = fsub double %4, %5
+  ret double %6
+}