Jakob Stoklund Olesen
8 years ago
12 changed files with 227 additions and 45 deletions
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//! Memory operation flags.
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use std::fmt; |
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enum FlagBit { |
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Notrap, |
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Aligned, |
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} |
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const NAMES: [&'static str; 2] = ["notrap", "aligned"]; |
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/// Flags for memory operations like load/store.
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///
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/// Each of these flags introduce a limited form of undefined behavior. The flags each enable
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/// certain optimizations that need to make additional assumptions. Generally, the semantics of a
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/// program does not change when a flag is removed, but adding a flag will.
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#[derive(Clone, Copy, Debug)] |
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pub struct MemFlags { |
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bits: u8, |
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} |
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impl MemFlags { |
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/// Create a new empty set of flags.
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pub fn new() -> MemFlags { |
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MemFlags { bits: 0 } |
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} |
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/// Read a flag bit.
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fn read(self, bit: FlagBit) -> bool { |
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self.bits & (1 << bit as usize) != 0 |
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} |
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/// Set a flag bit.
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fn set(&mut self, bit: FlagBit) { |
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self.bits |= 1 << bit as usize |
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} |
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/// Set a flag bit by name.
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///
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/// Returns true if the flag was found and set, false for an unknown flag name.
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pub fn set_by_name(&mut self, name: &str) -> bool { |
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match NAMES.iter().position(|&s| s == name) { |
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Some(bit) => { |
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self.bits |= 1 << bit; |
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true |
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} |
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None => false, |
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} |
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} |
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/// Test if the `notrap` flag is set.
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///
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/// Normally, trapping is part of the semantics of a load/store operation. If the platform
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/// would cause a trap when accessing the effective address, the Cretonne memory operation is
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/// also required to trap.
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///
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/// The `notrap` flag gives a Cretonne operation permission to not trap. This makes it possible
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/// to delete an unused load or a dead store instruction.
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pub fn notrap(self) -> bool { |
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self.read(FlagBit::Notrap) |
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} |
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/// Set the `notrap` flag.
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pub fn set_notrap(&mut self) { |
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self.set(FlagBit::Notrap) |
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} |
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/// Test if the `aligned` flag is set.
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///
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/// By default, Cretonne memory instructions work with any unaligned effective address. If the
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/// `aligned` flag is set, the instruction is permitted to trap or return a wrong result if the
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/// effective address is misaligned.
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pub fn aligned(self) -> bool { |
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self.read(FlagBit::Aligned) |
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} |
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/// Set the `aligned` flag.
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pub fn set_aligned(&mut self) { |
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self.set(FlagBit::Aligned) |
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} |
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} |
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impl fmt::Display for MemFlags { |
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { |
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for (i, n) in NAMES.iter().enumerate() { |
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if self.bits & (1 << i) != 0 { |
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write!(f, " {}", n)?; |
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} |
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} |
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Ok(()) |
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} |
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} |
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