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disable ConstProp of floats #113416

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disable ConstProp of floats #113416

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44c6999
disable ConstProp of floats
RalfJung Jul 6, 2023
797ebf5
add tests
RalfJung Jul 7, 2023
7153840
move misplaced tests
RalfJung Jul 7, 2023
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8 changes: 8 additions & 0 deletions compiler/rustc_mir_transform/src/const_prop.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -520,6 +520,14 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
rvalue: &Rvalue<'tcx>,
place: Place<'tcx>,
) -> Option<()> {
if place.ty(&self.ecx.frame().body.local_decls, *self.ecx.tcx).ty.is_floating_point() {
// Our apfloat is old and buggy (https://github.com/rust-lang/rust/issues/113409).
// Let's not risk wrong optimization results -- just do nothing for floats.
// This affects at least binary ops and casts, so just skip all rvalues.
// LLVM has a less buggy apfloat and will take care of const-propagation.
return None;
}

match rvalue {
Rvalue::BinaryOp(op, box (left, right))
| Rvalue::CheckedBinaryOp(op, box (left, right)) => {
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8 changes: 8 additions & 0 deletions compiler/rustc_mir_transform/src/dataflow_const_prop.rs
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Expand Up @@ -193,6 +193,14 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
rvalue: &Rvalue<'tcx>,
state: &mut State<Self::Value>,
) -> ValueOrPlace<Self::Value> {
if rvalue.ty(self.local_decls, self.tcx).is_floating_point() {
// Our apfloat is old and buggy (https://github.com/rust-lang/rust/issues/113409).
// Let's not risk wrong optimization results -- just do nothing for floats.
// This affects at least binary ops and casts, so just skip all rvalues.
// LLVM has a less buggy apfloat and will take care of const-propagation.
return ValueOrPlace::TOP;
}
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Maybe it is better to short-circuit in handle_rvalue then. But it would really help if the docs said whether TOP or BOTTOM represents "could be any value, statically unknown"...


match rvalue {
Rvalue::Cast(
kind @ (CastKind::IntToInt
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