[const-prop] Handle remaining MIR Rvalue cases #64890
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@@ -8,7 +8,7 @@ use rustc::hir::def::DefKind; | |
| use rustc::hir::def_id::DefId; | ||
| use rustc::mir::{ | ||
| AggregateKind, Constant, Location, Place, PlaceBase, Body, Operand, Rvalue, | ||
| Local, UnOp, StatementKind, Statement, LocalKind, | ||
| TerminatorKind, Terminator, ClearCrossCrate, SourceInfo, BinOp, | ||
| SourceScope, SourceScopeLocalData, LocalDecl, BasicBlock, | ||
| }; | ||
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@@ -118,7 +118,7 @@ impl<'tcx> MirPass<'tcx> for ConstProp { | |
| struct ConstPropMachine; | ||
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| impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine { | ||
| type MemoryKinds = !; | ||
| type PointerTag = (); | ||
| type ExtraFnVal = !; | ||
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@@ -434,32 +434,23 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { | |
| ) -> Option<Const<'tcx>> { | ||
| let span = source_info.span; | ||
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| let overflow_check = self.tcx.sess.overflow_checks(); | ||
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| // Perform any special handling for specific Rvalue types. | ||
| // Generally, checks here fall into one of two categories: | ||
| // 1. Additional checking to provide useful lints to the user | ||
| // - In this case, we will do some validation and then fall through to the | ||
| // end of the function which evals the assignment. | ||
| // 2. Working around bugs in other parts of the compiler | ||
| // - In this case, we'll return `None` from this function to stop evaluation. | ||
| match rvalue { | ||
| // Additional checking: if overflow checks are disabled (which is usually the case in | ||
| // release mode), then we need to do additional checking here to give lints to the user | ||
| // if an overflow would occur. | ||
| Rvalue::UnaryOp(UnOp::Neg, arg) if !overflow_check => { | ||
| trace!("checking UnaryOp(op = Neg, arg = {:?})", arg); | ||
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| self.use_ecx(source_info, |this| { | ||
| let ty = arg.ty(&this.local_decls, this.tcx); | ||
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| if ty.is_integral() { | ||
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@@ -471,60 +462,70 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { | |
| throw_panic!(OverflowNeg) | ||
| } | ||
| } | ||
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| Ok(()) | ||
| })?; | ||
| } | ||
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| // Additional checking: check for overflows on integer binary operations and report | ||
| // them to the user as lints. | ||
| Rvalue::BinaryOp(op, left, right) => { | ||
| trace!("checking BinaryOp(op = {:?}, left = {:?}, right = {:?})", op, left, right); | ||
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| let r = self.use_ecx(source_info, |this| { | ||
| this.ecx.read_immediate(this.ecx.eval_operand(right, None)?) | ||
| })?; | ||
| if *op == BinOp::Shr || *op == BinOp::Shl { | ||
| let left_bits = place_layout.size.bits(); | ||
| let right_size = r.layout.size; | ||
| let r_bits = r.to_scalar().and_then(|r| r.to_bits(right_size)); | ||
| if r_bits.ok().map_or(false, |b| b >= left_bits as u128) { | ||
| let source_scope_local_data = match self.source_scope_local_data { | ||
| ClearCrossCrate::Set(ref data) => data, | ||
| ClearCrossCrate::Clear => return None, | ||
| }; | ||
| let dir = if *op == BinOp::Shr { | ||
| "right" | ||
| } else { | ||
| "left" | ||
| }; | ||
| let hir_id = source_scope_local_data[source_info.scope].lint_root; | ||
| self.tcx.lint_hir( | ||
| ::rustc::lint::builtin::EXCEEDING_BITSHIFTS, | ||
| hir_id, | ||
| span, | ||
| &format!("attempt to shift {} with overflow", dir)); | ||
| return None; | ||
| } | ||
| } | ||
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| // If overflow checking is enabled (like in debug mode by default), | ||
| // then we'll already catch overflow when we evaluate the `Assert` statement | ||
| // in MIR. However, if overflow checking is disabled, then there won't be any | ||
| // `Assert` statement and so we have to do additional checking here. | ||
| if !overflow_check { | ||
| self.use_ecx(source_info, |this| { | ||
| let l = this.ecx.read_immediate(this.ecx.eval_operand(left, None)?)?; | ||
| let (_, overflow, _ty) = this.ecx.overflowing_binary_op(*op, l, r)?; | ||
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| if overflow { | ||
| let err = err_panic!(Overflow(*op)).into(); | ||
| return Err(err); | ||
| } | ||
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| Ok(()) | ||
| })?; | ||
| } | ||
| } | ||
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| // Work around: avoid ICE in miri. | ||
| // FIXME(wesleywiser) we don't currently handle the case where we try to make a ref | ||
| // from a function argument that hasn't been assigned to in this function. The main | ||
| // issue is if an arg is a fat-pointer, miri `expects()` to be able to read the value | ||
| // of that pointer to get size info. However, since this is `ConstProp`, that argument | ||
| // doesn't actually have a backing value and so this causes an ICE. | ||
| Rvalue::Ref(_, _, Place { base: PlaceBase::Local(local), projection: box [] }) => { | ||
| trace!("checking Ref({:?})", place); | ||
| let alive = | ||
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| if let LocalValue::Live(_) = self.ecx.frame().locals[*local].value { | ||
| true | ||
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@@ -535,6 +536,15 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> { | |
| return None; | ||
| } | ||
| } | ||
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| // Work around: avoid extra unnecessary locals. | ||
| // FIXME(wesleywiser): const eval will turn this into a `const Scalar(<ZST>)` that | ||
| // `SimplifyLocals` doesn't know it can remove. | ||
| Rvalue::Aggregate(_, operands) if operands.len() == 0 => { | ||
| return None; | ||
| } | ||
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| _ => { } | ||
| } | ||
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| self.use_ecx(source_info, |this| { | ||
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,25 @@ | ||
| // compile-flags: -O | ||
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| fn main() { | ||
| let x = (0, 1, 2).1 + 0; | ||
| } | ||
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| // END RUST SOURCE | ||
| // START rustc.main.ConstProp.before.mir | ||
| // bb0: { | ||
| // ... | ||
| // _3 = (const 0i32, const 1i32, const 2i32); | ||
| // _2 = (_3.1: i32); | ||
| // _1 = Add(move _2, const 0i32); | ||
| // ... | ||
| // } | ||
| // END rustc.main.ConstProp.before.mir | ||
| // START rustc.main.ConstProp.after.mir | ||
| // bb0: { | ||
| // ... | ||
| // _3 = (const 0i32, const 1i32, const 2i32); | ||
| // _2 = const 1i32; | ||
| // _1 = Add(move _2, const 0i32); | ||
| // ... | ||
| // } | ||
| // END rustc.main.ConstProp.after.mir |
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