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codegen: tweak/extend shift comments · rust-lang/rust@17bd43c

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  • compiler/rustc_codegen_ssa/src

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lines changed

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@@ -293,12 +293,13 @@ pub fn coerce_unsized_into<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(

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}

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}

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/// Returns `rhs` sufficiently masked, truncated, and/or extended so that

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/// it can be used to shift `lhs`.

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/// Returns `rhs` sufficiently masked, truncated, and/or extended so that it can be used to shift

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/// `lhs`: it has the same size as `lhs`, and the value, when interpreted unsigned (no matter its

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/// type), will not exceed the size of `lhs`.

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///

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/// Shifts in MIR are all allowed to have mismatched LHS & RHS types.

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/// Shifts in MIR are all allowed to have mismatched LHS & RHS types, and signed RHS.

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/// The shift methods in `BuilderMethods`, however, are fully homogeneous

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/// (both parameters and the return type are all the same type).

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/// (both parameters and the return type are all the same size) and assume an unsigned RHS.

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///

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/// If `is_unchecked` is false, this masks the RHS to ensure it stays in-bounds,

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/// as the `BuilderMethods` shifts are UB for out-of-bounds shift amounts.

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@@ -110,8 +110,16 @@ pub trait BuilderMethods<'a, 'tcx>:

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fn frem(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;

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fn frem_fast(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;

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fn frem_algebraic(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;

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/// Generate a left-shift. Both operands must have the same size. The right operand must be

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/// interpreted as unsigned and can be assumed to be less than the size of the left operand.

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fn shl(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;

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/// Generate a logical right-shift. Both operands must have the same size. The right operand

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/// must be interpreted as unsigned and can be assumed to be less than the size of the left

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/// operand.

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fn lshr(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;

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/// Generate an arithmetic right-shift. Both operands must have the same size. The right operand

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/// must be interpreted as unsigned and can be assumed to be less than the size of the left

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/// operand.

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fn ashr(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;

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fn unchecked_sadd(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;

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fn unchecked_uadd(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;