1 use crate::bitset::BitSet; 2 use crate::ir; 3 use crate::isa::TargetIsa; 4 use alloc::vec::Vec; 5 6 type Num = u32; 7 const NUM_BITS: usize = core::mem::size_of::<Num>() * 8; 8 9 /// A stack map is a bitmap with one bit per machine word on the stack. Stack 10 /// maps are created at `safepoint` instructions and record all live reference 11 /// values that are on the stack. All slot kinds, except `OutgoingArg` are 12 /// captured in a stack map. The `OutgoingArg`'s will be captured in the callee 13 /// function as `IncomingArg`'s. 14 /// 15 /// The first value in the bitmap is of the lowest addressed slot on the stack. 16 /// As all stacks in Isa's supported by Cranelift grow down, this means that 17 /// first value is of the top of the stack and values proceed down the stack. 18 #[derive(Clone, Debug)] 19 pub struct Stackmap { 20 bitmap: Vec<BitSet<Num>>, 21 mapped_words: u32, 22 } 23 24 impl Stackmap { 25 /// Create a stackmap based on where references are located on a function's stack. from_values( args: &[ir::entities::Value], func: &ir::Function, isa: &dyn TargetIsa, ) -> Self26 pub fn from_values( 27 args: &[ir::entities::Value], 28 func: &ir::Function, 29 isa: &dyn TargetIsa, 30 ) -> Self { 31 let loc = &func.locations; 32 let mut live_ref_in_stack_slot = crate::HashSet::new(); 33 // References can be in registers, and live registers values are pushed onto the stack before calls and traps. 34 // TODO: Implement register maps. If a register containing a reference is spilled and reused after a safepoint, 35 // it could contain a stale reference value if the garbage collector relocated the value. 36 for val in args { 37 if let Some(value_loc) = loc.get(*val) { 38 match *value_loc { 39 ir::ValueLoc::Stack(stack_slot) => { 40 live_ref_in_stack_slot.insert(stack_slot); 41 } 42 _ => {} 43 } 44 } 45 } 46 47 let stack = &func.stack_slots; 48 let info = func.stack_slots.layout_info.unwrap(); 49 50 // Refer to the doc comment for `Stackmap` above to understand the 51 // bitmap representation used here. 52 let map_size = (info.frame_size + info.inbound_args_size) as usize; 53 let word_size = isa.pointer_bytes() as usize; 54 let num_words = map_size / word_size; 55 56 let mut vec = alloc::vec::Vec::with_capacity(num_words); 57 vec.resize(num_words, false); 58 59 for (ss, ssd) in stack.iter() { 60 if !live_ref_in_stack_slot.contains(&ss) 61 || ssd.kind == ir::stackslot::StackSlotKind::OutgoingArg 62 { 63 continue; 64 } 65 66 debug_assert!(ssd.size as usize == word_size); 67 let bytes_from_bottom = info.frame_size as i32 + ssd.offset.unwrap(); 68 let words_from_bottom = (bytes_from_bottom as usize) / word_size; 69 vec[words_from_bottom] = true; 70 } 71 72 Self::from_slice(&vec) 73 } 74 75 /// Create a vec of Bitsets from a slice of bools. from_slice(vec: &[bool]) -> Self76 pub fn from_slice(vec: &[bool]) -> Self { 77 let len = vec.len(); 78 let num_word = len / NUM_BITS + (len % NUM_BITS != 0) as usize; 79 let mut bitmap = Vec::with_capacity(num_word); 80 81 for segment in vec.chunks(NUM_BITS) { 82 let mut curr_word = 0; 83 for (i, set) in segment.iter().enumerate() { 84 if *set { 85 curr_word |= 1 << i; 86 } 87 } 88 bitmap.push(BitSet(curr_word)); 89 } 90 Self { 91 mapped_words: len as u32, 92 bitmap, 93 } 94 } 95 96 /// Returns a specified bit. get_bit(&self, bit_index: usize) -> bool97 pub fn get_bit(&self, bit_index: usize) -> bool { 98 assert!(bit_index < NUM_BITS * self.bitmap.len()); 99 let word_index = bit_index / NUM_BITS; 100 let word_offset = (bit_index % NUM_BITS) as u8; 101 self.bitmap[word_index].contains(word_offset) 102 } 103 104 /// Returns the raw bitmap that represents this stack map. as_slice(&self) -> &[BitSet<u32>]105 pub fn as_slice(&self) -> &[BitSet<u32>] { 106 &self.bitmap 107 } 108 109 /// Returns the number of words represented by this stack map. mapped_words(&self) -> u32110 pub fn mapped_words(&self) -> u32 { 111 self.mapped_words 112 } 113 } 114 115 #[cfg(test)] 116 mod tests { 117 use super::*; 118 119 #[test] stackmaps()120 fn stackmaps() { 121 let vec: Vec<bool> = Vec::new(); 122 assert!(Stackmap::from_slice(&vec).bitmap.is_empty()); 123 124 let mut vec: [bool; NUM_BITS] = Default::default(); 125 let set_true_idx = [5, 7, 24, 31]; 126 127 for &idx in &set_true_idx { 128 vec[idx] = true; 129 } 130 131 let mut vec = vec.to_vec(); 132 assert_eq!( 133 vec![BitSet::<Num>(2164261024)], 134 Stackmap::from_slice(&vec).bitmap 135 ); 136 137 vec.push(false); 138 vec.push(true); 139 let res = Stackmap::from_slice(&vec); 140 assert_eq!( 141 vec![BitSet::<Num>(2164261024), BitSet::<Num>(2)], 142 res.bitmap 143 ); 144 145 assert!(res.get_bit(5)); 146 assert!(res.get_bit(31)); 147 assert!(res.get_bit(33)); 148 assert!(!res.get_bit(1)); 149 } 150 } 151