Auto merge of #111568 - scottmcm:undo-opt, r=WaffleLapkin
Stop turning transmutes into discriminant reads in mir-opt Partially reverts #109612, as after #109993 these aren't actually equivalent any more, and I'm no longer confident this was ever an improvement in the first place. Having this "simplification" meant that similar-looking code actually did somewhat different things. For example, ```rust pub unsafe fn demo1(x: std::cmp::Ordering) -> u8 { std::mem::transmute(x) } pub unsafe fn demo2(x: std::cmp::Ordering) -> i8 { std::mem::transmute(x) } ``` in nightly today is generating <https://rust.godbolt.org/z/dPK58zW18> ```llvm define noundef i8 `@_ZN7example5demo117h341ef313673d2ee6E(i8` noundef %x) unnamed_addr #0 { %0 = icmp uge i8 %x, -1 %1 = icmp ule i8 %x, 1 %2 = or i1 %0, %1 call void `@llvm.assume(i1` %2) ret i8 %x } define noundef i8 `@_ZN7example5demo217h5ad29f361a3f5700E(i8` noundef %0) unnamed_addr #0 { %x = alloca i8, align 1 store i8 %0, ptr %x, align 1 %1 = load i8, ptr %x, align 1, !range !2, !noundef !3 ret i8 %1 } ``` Which feels too different when the original code is essentially identical. --- Aside: that example is different *after* optimizations too: ```llvm define noundef i8 `@_ZN7example5demo117h341ef313673d2ee6E(i8` noundef returned %x) unnamed_addr #0 { %0 = add i8 %x, 1 %1 = icmp ult i8 %0, 3 tail call void `@llvm.assume(i1` %1) ret i8 %x } define noundef i8 `@_ZN7example5demo217h5ad29f361a3f5700E(i8` noundef returned %0) unnamed_addr #1 { ret i8 %0 } ``` so turning the `Transmute` into a `Discriminant` was arguably just making things worse, so leaving it alone instead -- and thus having less code in rustc -- seems clearly better.
This commit is contained in:
bors
commit
e9e1bbc7a8
@ -5,7 +5,6 @@
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use rustc_hir::Mutability;
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use rustc_middle::mir::*;
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use rustc_middle::ty::layout::ValidityRequirement;
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use rustc_middle::ty::util::IntTypeExt;
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use rustc_middle::ty::{self, ParamEnv, SubstsRef, Ty, TyCtxt};
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use rustc_span::symbol::Symbol;
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use rustc_target::abi::FieldIdx;
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@ -163,18 +162,6 @@ fn simplify_cast(&self, _source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
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return;
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}
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// Transmuting a fieldless enum to its repr is a discriminant read
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if let ty::Adt(adt_def, ..) = operand_ty.kind()
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&& adt_def.is_enum()
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&& adt_def.is_payloadfree()
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&& let Some(place) = operand.place()
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&& let Some(repr_int) = adt_def.repr().int
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&& repr_int.to_ty(self.tcx) == *cast_ty
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{
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*rvalue = Rvalue::Discriminant(place);
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return;
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}
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// Transmuting a transparent struct/union to a field's type is a projection
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if let ty::Adt(adt_def, substs) = operand_ty.kind()
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&& adt_def.repr().transparent()
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@ -4,59 +4,29 @@
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fn adt_transmutes() -> () {
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let mut _0: (); // return place in scope 0 at $DIR/combine_transmutes.rs:+0:32: +0:32
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let _1: u8; // in scope 0 at $DIR/combine_transmutes.rs:+1:9: +1:11
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let mut _2: EnumNoRepr; // in scope 0 at $DIR/combine_transmutes.rs:+1:28: +1:41
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let mut _4: EnumNoRepr; // in scope 0 at $DIR/combine_transmutes.rs:+2:28: +2:41
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let mut _6: EnumReprIsize; // in scope 0 at $DIR/combine_transmutes.rs:+3:31: +3:47
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let mut _8: EnumReprIsize; // in scope 0 at $DIR/combine_transmutes.rs:+4:31: +4:47
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let mut _10: std::cmp::Ordering; // in scope 0 at $DIR/combine_transmutes.rs:+5:28: +5:52
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let mut _12: std::cmp::Ordering; // in scope 0 at $DIR/combine_transmutes.rs:+6:28: +6:52
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let mut _14: std::option::Option<std::num::NonZeroU8>; // in scope 0 at $DIR/combine_transmutes.rs:+7:28: +7:58
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let mut _16: std::num::Wrapping<i16>; // in scope 0 at $DIR/combine_transmutes.rs:+8:29: +8:54
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let mut _18: std::num::Wrapping<i16>; // in scope 0 at $DIR/combine_transmutes.rs:+9:29: +9:54
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let mut _20: Union32; // in scope 0 at $DIR/combine_transmutes.rs:+10:29: +10:47
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let mut _22: Union32; // in scope 0 at $DIR/combine_transmutes.rs:+11:29: +11:47
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let mut _24: std::mem::MaybeUninit<std::string::String>; // in scope 0 at $DIR/combine_transmutes.rs:+12:46: +12:77
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let mut _2: std::option::Option<std::num::NonZeroU8>; // in scope 0 at $DIR/combine_transmutes.rs:+1:28: +1:58
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let mut _4: std::num::Wrapping<i16>; // in scope 0 at $DIR/combine_transmutes.rs:+2:29: +2:54
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let mut _6: std::num::Wrapping<i16>; // in scope 0 at $DIR/combine_transmutes.rs:+3:29: +3:54
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let mut _8: Union32; // in scope 0 at $DIR/combine_transmutes.rs:+4:29: +4:47
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let mut _10: Union32; // in scope 0 at $DIR/combine_transmutes.rs:+5:29: +5:47
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let mut _12: std::mem::MaybeUninit<std::string::String>; // in scope 0 at $DIR/combine_transmutes.rs:+6:46: +6:77
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scope 1 {
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debug _a => _1; // in scope 1 at $DIR/combine_transmutes.rs:+1:9: +1:11
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let _3: i8; // in scope 1 at $DIR/combine_transmutes.rs:+2:9: +2:11
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let _3: i16; // in scope 1 at $DIR/combine_transmutes.rs:+2:9: +2:11
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scope 2 {
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debug _a => _3; // in scope 2 at $DIR/combine_transmutes.rs:+2:9: +2:11
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let _5: usize; // in scope 2 at $DIR/combine_transmutes.rs:+3:9: +3:11
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let _5: u16; // in scope 2 at $DIR/combine_transmutes.rs:+3:9: +3:11
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scope 3 {
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debug _a => _5; // in scope 3 at $DIR/combine_transmutes.rs:+3:9: +3:11
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let _7: isize; // in scope 3 at $DIR/combine_transmutes.rs:+4:9: +4:11
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let _7: u32; // in scope 3 at $DIR/combine_transmutes.rs:+4:9: +4:11
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scope 4 {
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debug _a => _7; // in scope 4 at $DIR/combine_transmutes.rs:+4:9: +4:11
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let _9: u8; // in scope 4 at $DIR/combine_transmutes.rs:+5:9: +5:11
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let _9: i32; // in scope 4 at $DIR/combine_transmutes.rs:+5:9: +5:11
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scope 5 {
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debug _a => _9; // in scope 5 at $DIR/combine_transmutes.rs:+5:9: +5:11
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let _11: i8; // in scope 5 at $DIR/combine_transmutes.rs:+6:9: +6:11
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let _11: std::mem::ManuallyDrop<std::string::String>; // in scope 5 at $DIR/combine_transmutes.rs:+6:9: +6:11
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scope 6 {
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debug _a => _11; // in scope 6 at $DIR/combine_transmutes.rs:+6:9: +6:11
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let _13: u8; // in scope 6 at $DIR/combine_transmutes.rs:+7:9: +7:11
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scope 7 {
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debug _a => _13; // in scope 7 at $DIR/combine_transmutes.rs:+7:9: +7:11
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let _15: i16; // in scope 7 at $DIR/combine_transmutes.rs:+8:9: +8:11
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scope 8 {
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debug _a => _15; // in scope 8 at $DIR/combine_transmutes.rs:+8:9: +8:11
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let _17: u16; // in scope 8 at $DIR/combine_transmutes.rs:+9:9: +9:11
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scope 9 {
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debug _a => _17; // in scope 9 at $DIR/combine_transmutes.rs:+9:9: +9:11
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let _19: u32; // in scope 9 at $DIR/combine_transmutes.rs:+10:9: +10:11
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scope 10 {
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debug _a => _19; // in scope 10 at $DIR/combine_transmutes.rs:+10:9: +10:11
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let _21: i32; // in scope 10 at $DIR/combine_transmutes.rs:+11:9: +11:11
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scope 11 {
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debug _a => _21; // in scope 11 at $DIR/combine_transmutes.rs:+11:9: +11:11
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let _23: std::mem::ManuallyDrop<std::string::String>; // in scope 11 at $DIR/combine_transmutes.rs:+12:9: +12:11
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scope 12 {
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debug _a => _23; // in scope 12 at $DIR/combine_transmutes.rs:+12:9: +12:11
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}
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}
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}
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}
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}
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}
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}
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}
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}
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@ -66,93 +36,55 @@
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bb0: {
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StorageLive(_1); // scope 0 at $DIR/combine_transmutes.rs:+1:9: +1:11
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StorageLive(_2); // scope 0 at $DIR/combine_transmutes.rs:+1:28: +1:41
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_2 = EnumNoRepr::A; // scope 0 at $DIR/combine_transmutes.rs:+1:28: +1:41
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_1 = move _2 as u8 (Transmute); // scope 0 at $DIR/combine_transmutes.rs:+1:18: +1:42
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StorageDead(_2); // scope 0 at $DIR/combine_transmutes.rs:+1:41: +1:42
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StorageLive(_2); // scope 0 at $DIR/combine_transmutes.rs:+1:28: +1:58
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_2 = Option::<NonZeroU8>::Some(const _); // scope 0 at $DIR/combine_transmutes.rs:+1:28: +1:58
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// mir::Constant
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// + span: $DIR/combine_transmutes.rs:35:33: 35:57
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// + literal: Const { ty: NonZeroU8, val: Unevaluated(NonZeroU8::MAX, [], None) }
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_1 = move _2 as u8 (Transmute); // scope 0 at $DIR/combine_transmutes.rs:+1:18: +1:59
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StorageDead(_2); // scope 0 at $DIR/combine_transmutes.rs:+1:58: +1:59
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StorageLive(_3); // scope 1 at $DIR/combine_transmutes.rs:+2:9: +2:11
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StorageLive(_4); // scope 1 at $DIR/combine_transmutes.rs:+2:28: +2:41
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_4 = EnumNoRepr::B; // scope 1 at $DIR/combine_transmutes.rs:+2:28: +2:41
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_3 = move _4 as i8 (Transmute); // scope 1 at $DIR/combine_transmutes.rs:+2:18: +2:42
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StorageDead(_4); // scope 1 at $DIR/combine_transmutes.rs:+2:41: +2:42
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StorageLive(_4); // scope 1 at $DIR/combine_transmutes.rs:+2:29: +2:54
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_4 = Wrapping::<i16>(const 0_i16); // scope 1 at $DIR/combine_transmutes.rs:+2:29: +2:54
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- _3 = move _4 as i16 (Transmute); // scope 1 at $DIR/combine_transmutes.rs:+2:19: +2:55
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+ _3 = move (_4.0: i16); // scope 1 at $DIR/combine_transmutes.rs:+2:19: +2:55
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StorageDead(_4); // scope 1 at $DIR/combine_transmutes.rs:+2:54: +2:55
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StorageLive(_5); // scope 2 at $DIR/combine_transmutes.rs:+3:9: +3:11
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StorageLive(_6); // scope 2 at $DIR/combine_transmutes.rs:+3:31: +3:47
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_6 = EnumReprIsize::A; // scope 2 at $DIR/combine_transmutes.rs:+3:31: +3:47
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_5 = move _6 as usize (Transmute); // scope 2 at $DIR/combine_transmutes.rs:+3:21: +3:48
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StorageDead(_6); // scope 2 at $DIR/combine_transmutes.rs:+3:47: +3:48
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StorageLive(_6); // scope 2 at $DIR/combine_transmutes.rs:+3:29: +3:54
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_6 = Wrapping::<i16>(const 0_i16); // scope 2 at $DIR/combine_transmutes.rs:+3:29: +3:54
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_5 = move _6 as u16 (Transmute); // scope 2 at $DIR/combine_transmutes.rs:+3:19: +3:55
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StorageDead(_6); // scope 2 at $DIR/combine_transmutes.rs:+3:54: +3:55
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StorageLive(_7); // scope 3 at $DIR/combine_transmutes.rs:+4:9: +4:11
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StorageLive(_8); // scope 3 at $DIR/combine_transmutes.rs:+4:31: +4:47
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_8 = EnumReprIsize::B; // scope 3 at $DIR/combine_transmutes.rs:+4:31: +4:47
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- _7 = move _8 as isize (Transmute); // scope 3 at $DIR/combine_transmutes.rs:+4:21: +4:48
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+ _7 = discriminant(_8); // scope 3 at $DIR/combine_transmutes.rs:+4:21: +4:48
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StorageLive(_8); // scope 3 at $DIR/combine_transmutes.rs:+4:29: +4:47
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_8 = Union32 { u32: const 0_i32 }; // scope 3 at $DIR/combine_transmutes.rs:+4:29: +4:47
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_7 = move _8 as u32 (Transmute); // scope 3 at $DIR/combine_transmutes.rs:+4:19: +4:48
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StorageDead(_8); // scope 3 at $DIR/combine_transmutes.rs:+4:47: +4:48
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StorageLive(_9); // scope 4 at $DIR/combine_transmutes.rs:+5:9: +5:11
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StorageLive(_10); // scope 4 at $DIR/combine_transmutes.rs:+5:28: +5:52
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_10 = Less; // scope 4 at $DIR/combine_transmutes.rs:+5:28: +5:52
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_9 = move _10 as u8 (Transmute); // scope 4 at $DIR/combine_transmutes.rs:+5:18: +5:53
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StorageDead(_10); // scope 4 at $DIR/combine_transmutes.rs:+5:52: +5:53
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StorageLive(_10); // scope 4 at $DIR/combine_transmutes.rs:+5:29: +5:47
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_10 = Union32 { u32: const 0_u32 }; // scope 4 at $DIR/combine_transmutes.rs:+5:29: +5:47
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_9 = move _10 as i32 (Transmute); // scope 4 at $DIR/combine_transmutes.rs:+5:19: +5:48
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StorageDead(_10); // scope 4 at $DIR/combine_transmutes.rs:+5:47: +5:48
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StorageLive(_11); // scope 5 at $DIR/combine_transmutes.rs:+6:9: +6:11
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StorageLive(_12); // scope 5 at $DIR/combine_transmutes.rs:+6:28: +6:52
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_12 = Less; // scope 5 at $DIR/combine_transmutes.rs:+6:28: +6:52
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- _11 = move _12 as i8 (Transmute); // scope 5 at $DIR/combine_transmutes.rs:+6:18: +6:53
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+ _11 = discriminant(_12); // scope 5 at $DIR/combine_transmutes.rs:+6:18: +6:53
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StorageDead(_12); // scope 5 at $DIR/combine_transmutes.rs:+6:52: +6:53
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StorageLive(_13); // scope 6 at $DIR/combine_transmutes.rs:+7:9: +7:11
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StorageLive(_14); // scope 6 at $DIR/combine_transmutes.rs:+7:28: +7:58
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_14 = Option::<NonZeroU8>::Some(const _); // scope 6 at $DIR/combine_transmutes.rs:+7:28: +7:58
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StorageLive(_12); // scope 5 at $DIR/combine_transmutes.rs:+6:46: +6:77
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_12 = MaybeUninit::<String>::uninit() -> [return: bb1, unwind unreachable]; // scope 5 at $DIR/combine_transmutes.rs:+6:46: +6:77
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// mir::Constant
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// + span: $DIR/combine_transmutes.rs:41:33: 41:57
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// + literal: Const { ty: NonZeroU8, val: Unevaluated(NonZeroU8::MAX, [], None) }
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_13 = move _14 as u8 (Transmute); // scope 6 at $DIR/combine_transmutes.rs:+7:18: +7:59
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StorageDead(_14); // scope 6 at $DIR/combine_transmutes.rs:+7:58: +7:59
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StorageLive(_15); // scope 7 at $DIR/combine_transmutes.rs:+8:9: +8:11
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StorageLive(_16); // scope 7 at $DIR/combine_transmutes.rs:+8:29: +8:54
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_16 = Wrapping::<i16>(const 0_i16); // scope 7 at $DIR/combine_transmutes.rs:+8:29: +8:54
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- _15 = move _16 as i16 (Transmute); // scope 7 at $DIR/combine_transmutes.rs:+8:19: +8:55
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+ _15 = move (_16.0: i16); // scope 7 at $DIR/combine_transmutes.rs:+8:19: +8:55
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StorageDead(_16); // scope 7 at $DIR/combine_transmutes.rs:+8:54: +8:55
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StorageLive(_17); // scope 8 at $DIR/combine_transmutes.rs:+9:9: +9:11
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StorageLive(_18); // scope 8 at $DIR/combine_transmutes.rs:+9:29: +9:54
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_18 = Wrapping::<i16>(const 0_i16); // scope 8 at $DIR/combine_transmutes.rs:+9:29: +9:54
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_17 = move _18 as u16 (Transmute); // scope 8 at $DIR/combine_transmutes.rs:+9:19: +9:55
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StorageDead(_18); // scope 8 at $DIR/combine_transmutes.rs:+9:54: +9:55
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StorageLive(_19); // scope 9 at $DIR/combine_transmutes.rs:+10:9: +10:11
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StorageLive(_20); // scope 9 at $DIR/combine_transmutes.rs:+10:29: +10:47
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_20 = Union32 { u32: const 0_i32 }; // scope 9 at $DIR/combine_transmutes.rs:+10:29: +10:47
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_19 = move _20 as u32 (Transmute); // scope 9 at $DIR/combine_transmutes.rs:+10:19: +10:48
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StorageDead(_20); // scope 9 at $DIR/combine_transmutes.rs:+10:47: +10:48
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StorageLive(_21); // scope 10 at $DIR/combine_transmutes.rs:+11:9: +11:11
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StorageLive(_22); // scope 10 at $DIR/combine_transmutes.rs:+11:29: +11:47
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_22 = Union32 { u32: const 0_u32 }; // scope 10 at $DIR/combine_transmutes.rs:+11:29: +11:47
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_21 = move _22 as i32 (Transmute); // scope 10 at $DIR/combine_transmutes.rs:+11:19: +11:48
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StorageDead(_22); // scope 10 at $DIR/combine_transmutes.rs:+11:47: +11:48
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StorageLive(_23); // scope 11 at $DIR/combine_transmutes.rs:+12:9: +12:11
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StorageLive(_24); // scope 11 at $DIR/combine_transmutes.rs:+12:46: +12:77
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_24 = MaybeUninit::<String>::uninit() -> [return: bb1, unwind unreachable]; // scope 11 at $DIR/combine_transmutes.rs:+12:46: +12:77
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// mir::Constant
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// + span: $DIR/combine_transmutes.rs:46:46: 46:75
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// + user_ty: UserType(23)
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// + span: $DIR/combine_transmutes.rs:40:46: 40:75
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// + user_ty: UserType(11)
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// + literal: Const { ty: fn() -> MaybeUninit<String> {MaybeUninit::<String>::uninit}, val: Value(<ZST>) }
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}
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bb1: {
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- _23 = move _24 as std::mem::ManuallyDrop<std::string::String> (Transmute); // scope 11 at $DIR/combine_transmutes.rs:+12:36: +12:78
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+ _23 = move (_24.1: std::mem::ManuallyDrop<std::string::String>); // scope 11 at $DIR/combine_transmutes.rs:+12:36: +12:78
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StorageDead(_24); // scope 11 at $DIR/combine_transmutes.rs:+12:77: +12:78
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_0 = const (); // scope 0 at $DIR/combine_transmutes.rs:+0:32: +13:2
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StorageDead(_23); // scope 11 at $DIR/combine_transmutes.rs:+13:1: +13:2
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StorageDead(_21); // scope 10 at $DIR/combine_transmutes.rs:+13:1: +13:2
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StorageDead(_19); // scope 9 at $DIR/combine_transmutes.rs:+13:1: +13:2
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StorageDead(_17); // scope 8 at $DIR/combine_transmutes.rs:+13:1: +13:2
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StorageDead(_15); // scope 7 at $DIR/combine_transmutes.rs:+13:1: +13:2
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StorageDead(_13); // scope 6 at $DIR/combine_transmutes.rs:+13:1: +13:2
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StorageDead(_11); // scope 5 at $DIR/combine_transmutes.rs:+13:1: +13:2
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StorageDead(_9); // scope 4 at $DIR/combine_transmutes.rs:+13:1: +13:2
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StorageDead(_7); // scope 3 at $DIR/combine_transmutes.rs:+13:1: +13:2
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||||
StorageDead(_5); // scope 2 at $DIR/combine_transmutes.rs:+13:1: +13:2
|
||||
StorageDead(_3); // scope 1 at $DIR/combine_transmutes.rs:+13:1: +13:2
|
||||
StorageDead(_1); // scope 0 at $DIR/combine_transmutes.rs:+13:1: +13:2
|
||||
return; // scope 0 at $DIR/combine_transmutes.rs:+13:2: +13:2
|
||||
- _11 = move _12 as std::mem::ManuallyDrop<std::string::String> (Transmute); // scope 5 at $DIR/combine_transmutes.rs:+6:36: +6:78
|
||||
+ _11 = move (_12.1: std::mem::ManuallyDrop<std::string::String>); // scope 5 at $DIR/combine_transmutes.rs:+6:36: +6:78
|
||||
StorageDead(_12); // scope 5 at $DIR/combine_transmutes.rs:+6:77: +6:78
|
||||
_0 = const (); // scope 0 at $DIR/combine_transmutes.rs:+0:32: +7:2
|
||||
StorageDead(_11); // scope 5 at $DIR/combine_transmutes.rs:+7:1: +7:2
|
||||
StorageDead(_9); // scope 4 at $DIR/combine_transmutes.rs:+7:1: +7:2
|
||||
StorageDead(_7); // scope 3 at $DIR/combine_transmutes.rs:+7:1: +7:2
|
||||
StorageDead(_5); // scope 2 at $DIR/combine_transmutes.rs:+7:1: +7:2
|
||||
StorageDead(_3); // scope 1 at $DIR/combine_transmutes.rs:+7:1: +7:2
|
||||
StorageDead(_1); // scope 0 at $DIR/combine_transmutes.rs:+7:1: +7:2
|
||||
return; // scope 0 at $DIR/combine_transmutes.rs:+7:2: +7:2
|
||||
}
|
||||
}
|
||||
|
||||
|
||||
@ -32,12 +32,6 @@ pub unsafe fn integer_transmutes() {
|
||||
|
||||
// EMIT_MIR combine_transmutes.adt_transmutes.InstSimplify.diff
|
||||
pub unsafe fn adt_transmutes() {
|
||||
let _a: u8 = transmute(EnumNoRepr::A);
|
||||
let _a: i8 = transmute(EnumNoRepr::B);
|
||||
let _a: usize = transmute(EnumReprIsize::A);
|
||||
let _a: isize = transmute(EnumReprIsize::B);
|
||||
let _a: u8 = transmute(std::cmp::Ordering::Less);
|
||||
let _a: i8 = transmute(std::cmp::Ordering::Less);
|
||||
let _a: u8 = transmute(Some(std::num::NonZeroU8::MAX));
|
||||
let _a: i16 = transmute(std::num::Wrapping(0_i16));
|
||||
let _a: u16 = transmute(std::num::Wrapping(0_i16));
|
||||
@ -46,20 +40,4 @@ pub unsafe fn adt_transmutes() {
|
||||
let _a: ManuallyDrop<String> = transmute(MaybeUninit::<String>::uninit());
|
||||
}
|
||||
|
||||
#[inline(always)]
|
||||
#[custom_mir(dialect = "runtime", phase = "initial")]
|
||||
const unsafe fn mir_transmute<T, U>(x: T) -> U {
|
||||
mir!{
|
||||
{
|
||||
RET = CastTransmute(x);
|
||||
Return()
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
pub enum EnumNoRepr { A, B, C }
|
||||
|
||||
#[repr(isize)]
|
||||
pub enum EnumReprIsize { A, B, C }
|
||||
|
||||
pub union Union32 { u32: u32, i32: i32 }
|
||||
|
||||
Loading…
Reference in New Issue
Block a user