[AArch64] Add getStreamingHazardSize() to AArch64Subtarget

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -126,14 +126,15 @@
 // and the SME unit try to access the same area of memory, including if the
 // access is to an area of the stack. To try to alleviate this we attempt to
 // introduce extra padding into the stack frame between FP and GPR accesses,
-// controlled by the StackHazardSize option. Without changing the layout of the
-// stack frame in the diagram above, a stack object of size StackHazardSize is
-// added between GPR and FPR CSRs. Another is added to the stack objects
-// section, and stack objects are sorted so that FPR > Hazard padding slot >
-// GPRs (where possible). Unfortunately some things are not handled well (VLA
-// area, arguments on the stack, object with both GPR and FPR accesses), but if
-// those are controlled by the user then the entire stack frame becomes GPR at
-// the start/end with FPR in the middle, surrounded by Hazard padding.
+// controlled by the aarch64-stack-hazard-size option. Without changing the
+// layout of the stack frame in the diagram above, a stack object of size
+// aarch64-stack-hazard-size is added between GPR and FPR CSRs. Another is added
+// to the stack objects section, and stack objects are sorted so that FPR >
+// Hazard padding slot > GPRs (where possible). Unfortunately some things are
+// not handled well (VLA area, arguments on the stack, objects with both GPR and
+// FPR accesses), but if those are controlled by the user then the entire stack
+// frame becomes GPR at the start/end with FPR in the middle, surrounded by
+// Hazard padding.
 //
 // An example of the prologue:
 //
@@ -273,9 +274,6 @@ cl::opt<bool> EnableHomogeneousPrologEpilog(
     cl::desc("Emit homogeneous prologue and epilogue for the size "
              "optimization (default = off)"));
 
-// Stack hazard padding size. 0 = disabled.
-static cl::opt<unsigned> StackHazardSize("aarch64-stack-hazard-size",
-                                         cl::init(0), cl::Hidden);
 // Stack hazard size for analysis remarks. StackHazardSize takes precedence.
 static cl::opt<unsigned>
     StackHazardRemarkSize("aarch64-stack-hazard-remark-size", cl::init(0),
@@ -1614,6 +1612,10 @@ static bool isTargetWindows(const MachineFunction &MF) {
   return MF.getSubtarget<AArch64Subtarget>().isTargetWindows();
 }
 
+static unsigned getStackHazardSize(const MachineFunction &MF) {
+  return MF.getSubtarget<AArch64Subtarget>().getStreamingHazardSize();
+}
+
 // Convenience function to determine whether I is an SVE callee save.
 static bool IsSVECalleeSave(MachineBasicBlock::iterator I) {
   switch (I->getOpcode()) {
@@ -2985,6 +2987,7 @@ static void computeCalleeSaveRegisterPairs(
   bool IsWindows = isTargetWindows(MF);
   bool NeedsWinCFI = needsWinCFI(MF);
   AArch64FunctionInfo *AFI = MF.getInfo<AArch64FunctionInfo>();
+  unsigned StackHazardSize = getStackHazardSize(MF);
   MachineFrameInfo &MFI = MF.getFrameInfo();
   CallingConv::ID CC = MF.getFunction().getCallingConv();
   unsigned Count = CSI.size();
@@ -3612,6 +3615,7 @@ static std::optional<int> getLdStFrameID(const MachineInstr &MI,
 // which can be used to determine if any hazard padding is needed.
 void AArch64FrameLowering::determineStackHazardSlot(
     MachineFunction &MF, BitVector &SavedRegs) const {
+  unsigned StackHazardSize = getStackHazardSize(MF);
   if (StackHazardSize == 0 || StackHazardSize % 16 != 0 ||
       MF.getInfo<AArch64FunctionInfo>()->hasStackHazardSlotIndex())
     return;
@@ -3802,7 +3806,7 @@ void AArch64FrameLowering::determineCalleeSaves(MachineFunction &MF,
   // StackHazardSize if so.
   determineStackHazardSlot(MF, SavedRegs);
   if (AFI->hasStackHazardSlotIndex())
-    CSStackSize += StackHazardSize;
+    CSStackSize += getStackHazardSize(MF);
 
   // Save number of saved regs, so we can easily update CSStackSize later.
   unsigned NumSavedRegs = SavedRegs.count();
@@ -3917,6 +3921,7 @@ bool AArch64FrameLowering::assignCalleeSavedSpillSlots(
     std::vector<CalleeSavedInfo> &CSI, unsigned &MinCSFrameIndex,
     unsigned &MaxCSFrameIndex) const {
   bool NeedsWinCFI = needsWinCFI(MF);
+  unsigned StackHazardSize = getStackHazardSize(MF);
   // To match the canonical windows frame layout, reverse the list of
   // callee saved registers to get them laid out by PrologEpilogInserter
   // in the right order. (PrologEpilogInserter allocates stack objects top
@@ -5151,6 +5156,7 @@ void AArch64FrameLowering::emitRemarks(
   if (Attrs.hasNonStreamingInterfaceAndBody())
     return;
 
+  unsigned StackHazardSize = getStackHazardSize(MF);
   const uint64_t HazardSize =
       (StackHazardSize) ? StackHazardSize : StackHazardRemarkSize;
 

llvm/lib/Target/AArch64/AArch64Subtarget.cpp

@@ -76,6 +76,16 @@ static cl::opt<unsigned> AArch64MinimumJumpTableEntries(
     "aarch64-min-jump-table-entries", cl::init(13), cl::Hidden,
     cl::desc("Set minimum number of entries to use a jump table on AArch64"));
 
+static cl::opt<unsigned> AArch64StreamingHazardSize(
+    "aarch64-streaming-hazard-size",
+    cl::desc("Hazard size for streaming mode memory accesses. 0 = disabled."),
+    cl::init(0), cl::Hidden);
+
+static cl::alias AArch64StreamingStackHazardSize(
+    "aarch64-stack-hazard-size",
+    cl::desc("alias for -aarch64-streaming-hazard-size"),
+    cl::aliasopt(AArch64StreamingHazardSize));
+
 unsigned AArch64Subtarget::getVectorInsertExtractBaseCost() const {
   if (OverrideVectorInsertExtractBaseCost.getNumOccurrences() > 0)
     return OverrideVectorInsertExtractBaseCost;
@@ -333,6 +343,7 @@ AArch64Subtarget::AArch64Subtarget(const Triple &TT, StringRef CPU,
       CustomCallSavedXRegs(AArch64::GPR64commonRegClass.getNumRegs()),
       IsLittle(LittleEndian), IsStreaming(IsStreaming),
       IsStreamingCompatible(IsStreamingCompatible),
+      StreamingHazardSize(AArch64StreamingHazardSize),
       MinSVEVectorSizeInBits(MinSVEVectorSizeInBitsOverride),
       MaxSVEVectorSizeInBits(MaxSVEVectorSizeInBitsOverride), TargetTriple(TT),
       InstrInfo(initializeSubtargetDependencies(FS, CPU, TuneCPU, HasMinSize)),

llvm/lib/Target/AArch64/AArch64Subtarget.h

@@ -84,6 +84,7 @@ class AArch64Subtarget final : public AArch64GenSubtargetInfo {
 
   bool IsStreaming;
   bool IsStreamingCompatible;
+  unsigned StreamingHazardSize;
   unsigned MinSVEVectorSizeInBits;
   unsigned MaxSVEVectorSizeInBits;
   unsigned VScaleForTuning = 2;
@@ -172,6 +173,10 @@ class AArch64Subtarget final : public AArch64GenSubtargetInfo {
   /// Returns true if the function has a streaming-compatible body.
   bool isStreamingCompatible() const { return IsStreamingCompatible; }
 
+  /// Returns the size of memory region that if accessed by both the CPU and
+  /// the SME unit could result in a hazard. 0 = disabled.
+  unsigned getStreamingHazardSize() const { return StreamingHazardSize; }
+
   /// Returns true if the target has NEON and the function at runtime is known
   /// to have NEON enabled (e.g. the function is known not to be in streaming-SVE
   /// mode, which disables NEON instructions).