Auto merge of #109993 - scottmcm:transmute-niches, r=oli-obk

`assume` value ranges in `transmute`

Fixes #109958

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -12,6 +12,7 @@ use rustc_middle::mir::Operand;
 use rustc_middle::ty::cast::{CastTy, IntTy};
 use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, TyAndLayout};
 use rustc_middle::ty::{self, adjustment::PointerCast, Instance, Ty, TyCtxt};
+use rustc_session::config::OptLevel;
 use rustc_span::source_map::{Span, DUMMY_SP};
 use rustc_target::abi::{self, FIRST_VARIANT};
 
@@ -231,10 +232,16 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         (ScalarOrZst::Scalar(in_scalar), ScalarOrZst::Scalar(out_scalar))
                             if in_scalar.size(self.cx) == out_scalar.size(self.cx) =>
                         {
+                            let operand_bty = bx.backend_type(operand.layout);
                             let cast_bty = bx.backend_type(cast);
-                            Some(OperandValue::Immediate(
-                                self.transmute_immediate(bx, imm, in_scalar, out_scalar, cast_bty),
-                            ))
+                            Some(OperandValue::Immediate(self.transmute_immediate(
+                                bx,
+                                imm,
+                                in_scalar,
+                                operand_bty,
+                                out_scalar,
+                                cast_bty,
+                            )))
                         }
                         _ => None,
                     }
@@ -250,11 +257,13 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     && in_a.size(self.cx) == out_a.size(self.cx)
                     && in_b.size(self.cx) == out_b.size(self.cx)
                 {
+                    let in_a_ibty = bx.scalar_pair_element_backend_type(operand.layout, 0, false);
+                    let in_b_ibty = bx.scalar_pair_element_backend_type(operand.layout, 1, false);
                     let out_a_ibty = bx.scalar_pair_element_backend_type(cast, 0, false);
                     let out_b_ibty = bx.scalar_pair_element_backend_type(cast, 1, false);
                     Some(OperandValue::Pair(
-                        self.transmute_immediate(bx, imm_a, in_a, out_a, out_a_ibty),
-                        self.transmute_immediate(bx, imm_b, in_b, out_b, out_b_ibty),
+                        self.transmute_immediate(bx, imm_a, in_a, in_a_ibty, out_a, out_a_ibty),
+                        self.transmute_immediate(bx, imm_b, in_b, in_b_ibty, out_b, out_b_ibty),
                     ))
                 } else {
                     None
@@ -273,6 +282,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         bx: &mut Bx,
         mut imm: Bx::Value,
         from_scalar: abi::Scalar,
+        from_backend_ty: Bx::Type,
         to_scalar: abi::Scalar,
         to_backend_ty: Bx::Type,
     ) -> Bx::Value {
@@ -280,6 +290,13 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
 
         use abi::Primitive::*;
         imm = bx.from_immediate(imm);
+
+        // When scalars are passed by value, there's no metadata recording their
+        // valid ranges. For example, `char`s are passed as just `i32`, with no
+        // way for LLVM to know that they're 0x10FFFF at most. Thus we assume
+        // the range of the input value too, not just the output range.
+        self.assume_scalar_range(bx, imm, from_scalar, from_backend_ty);
+
         imm = match (from_scalar.primitive(), to_scalar.primitive()) {
             (Int(..) | F32 | F64, Int(..) | F32 | F64) => bx.bitcast(imm, to_backend_ty),
             (Pointer(..), Pointer(..)) => bx.pointercast(imm, to_backend_ty),
@@ -294,10 +311,55 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 bx.bitcast(int_imm, to_backend_ty)
             }
         };
+        self.assume_scalar_range(bx, imm, to_scalar, to_backend_ty);
         imm = bx.to_immediate_scalar(imm, to_scalar);
         imm
     }
 
+    fn assume_scalar_range(
+        &self,
+        bx: &mut Bx,
+        imm: Bx::Value,
+        scalar: abi::Scalar,
+        backend_ty: Bx::Type,
+    ) {
+        if matches!(self.cx.sess().opts.optimize, OptLevel::No | OptLevel::Less)
+            // For now, the critical niches are all over `Int`eger values.
+            // Should floating-point values or pointers ever get more complex
+            // niches, then this code will probably want to handle them too.
+            || !matches!(scalar.primitive(), abi::Primitive::Int(..))
+            || scalar.is_always_valid(self.cx)
+        {
+            return;
+        }
+
+        let abi::WrappingRange { start, end } = scalar.valid_range(self.cx);
+
+        if start <= end {
+            if start > 0 {
+                let low = bx.const_uint_big(backend_ty, start);
+                let cmp = bx.icmp(IntPredicate::IntUGE, imm, low);
+                bx.assume(cmp);
+            }
+
+            let type_max = scalar.size(self.cx).unsigned_int_max();
+            if end < type_max {
+                let high = bx.const_uint_big(backend_ty, end);
+                let cmp = bx.icmp(IntPredicate::IntULE, imm, high);
+                bx.assume(cmp);
+            }
+        } else {
+            let low = bx.const_uint_big(backend_ty, start);
+            let cmp_low = bx.icmp(IntPredicate::IntUGE, imm, low);
+
+            let high = bx.const_uint_big(backend_ty, end);
+            let cmp_high = bx.icmp(IntPredicate::IntULE, imm, high);
+
+            let or = bx.or(cmp_low, cmp_high);
+            bx.assume(or);
+        }
+    }
+
     pub fn codegen_rvalue_unsized(
         &mut self,
         bx: &mut Bx,

tests/codegen/intrinsics/transmute-niched.rs

@@ -0,0 +1,184 @@
+// revisions: OPT DBG
+// [OPT] compile-flags: -C opt-level=3 -C no-prepopulate-passes
+// [DBG] compile-flags: -C opt-level=0 -C no-prepopulate-passes
+// only-64bit (so I don't need to worry about usize)
+// min-llvm-version: 15.0 # this test assumes `ptr`s
+
+#![crate_type = "lib"]
+
+use std::mem::transmute;
+use std::num::NonZeroU32;
+
+#[repr(u8)]
+pub enum SmallEnum {
+    A = 10,
+    B = 11,
+    C = 12,
+}
+
+// CHECK-LABEL: @check_to_enum(
+#[no_mangle]
+pub unsafe fn check_to_enum(x: i8) -> SmallEnum {
+    // OPT: %0 = icmp uge i8 %x, 10
+    // OPT: call void @llvm.assume(i1 %0)
+    // OPT: %1 = icmp ule i8 %x, 12
+    // OPT: call void @llvm.assume(i1 %1)
+    // DBG-NOT: icmp
+    // DBG-NOT: assume
+    // CHECK: ret i8 %x
+
+    transmute(x)
+}
+
+// CHECK-LABEL: @check_from_enum(
+#[no_mangle]
+pub unsafe fn check_from_enum(x: SmallEnum) -> i8 {
+    // OPT: %0 = icmp uge i8 %x, 10
+    // OPT: call void @llvm.assume(i1 %0)
+    // OPT: %1 = icmp ule i8 %x, 12
+    // OPT: call void @llvm.assume(i1 %1)
+    // DBG-NOT: icmp
+    // DBG-NOT: assume
+    // CHECK: ret i8 %x
+
+    transmute(x)
+}
+
+// CHECK-LABEL: @check_to_ordering(
+#[no_mangle]
+pub unsafe fn check_to_ordering(x: u8) -> std::cmp::Ordering {
+    // OPT: %0 = icmp uge i8 %x, -1
+    // OPT: %1 = icmp ule i8 %x, 1
+    // OPT: %2 = or i1 %0, %1
+    // OPT: call void @llvm.assume(i1 %2)
+    // DBG-NOT: icmp
+    // DBG-NOT: assume
+    // CHECK: ret i8 %x
+
+    transmute(x)
+}
+
+// CHECK-LABEL: @check_from_ordering(
+#[no_mangle]
+pub unsafe fn check_from_ordering(x: std::cmp::Ordering) -> u8 {
+    // OPT: %0 = icmp uge i8 %x, -1
+    // OPT: %1 = icmp ule i8 %x, 1
+    // OPT: %2 = or i1 %0, %1
+    // OPT: call void @llvm.assume(i1 %2)
+    // DBG-NOT: icmp
+    // DBG-NOT: assume
+    // CHECK: ret i8 %x
+
+    transmute(x)
+}
+
+#[repr(i32)]
+pub enum Minus100ToPlus100 {
+    A = -100,
+    B = -90,
+    C = -80,
+    D = -70,
+    E = -60,
+    F = -50,
+    G = -40,
+    H = -30,
+    I = -20,
+    J = -10,
+    K = 0,
+    L = 10,
+    M = 20,
+    N = 30,
+    O = 40,
+    P = 50,
+    Q = 60,
+    R = 70,
+    S = 80,
+    T = 90,
+    U = 100,
+}
+
+// CHECK-LABEL: @check_enum_from_char(
+#[no_mangle]
+pub unsafe fn check_enum_from_char(x: char) -> Minus100ToPlus100 {
+    // OPT: %0 = icmp ule i32 %x, 1114111
+    // OPT: call void @llvm.assume(i1 %0)
+    // OPT: %1 = icmp uge i32 %x, -100
+    // OPT: %2 = icmp ule i32 %x, 100
+    // OPT: %3 = or i1 %1, %2
+    // OPT: call void @llvm.assume(i1 %3)
+    // DBG-NOT: icmp
+    // DBG-NOT: assume
+    // CHECK: ret i32 %x
+
+    transmute(x)
+}
+
+// CHECK-LABEL: @check_enum_to_char(
+#[no_mangle]
+pub unsafe fn check_enum_to_char(x: Minus100ToPlus100) -> char {
+    // OPT: %0 = icmp uge i32 %x, -100
+    // OPT: %1 = icmp ule i32 %x, 100
+    // OPT: %2 = or i1 %0, %1
+    // OPT: call void @llvm.assume(i1 %2)
+    // OPT: %3 = icmp ule i32 %x, 1114111
+    // OPT: call void @llvm.assume(i1 %3)
+    // DBG-NOT: icmp
+    // DBG-NOT: assume
+    // CHECK: ret i32 %x
+
+    transmute(x)
+}
+
+// CHECK-LABEL: @check_swap_pair(
+#[no_mangle]
+pub unsafe fn check_swap_pair(x: (char, NonZeroU32)) -> (NonZeroU32, char) {
+    // OPT: %0 = icmp ule i32 %x.0, 1114111
+    // OPT: call void @llvm.assume(i1 %0)
+    // OPT: %1 = icmp uge i32 %x.0, 1
+    // OPT: call void @llvm.assume(i1 %1)
+    // OPT: %2 = icmp uge i32 %x.1, 1
+    // OPT: call void @llvm.assume(i1 %2)
+    // OPT: %3 = icmp ule i32 %x.1, 1114111
+    // OPT: call void @llvm.assume(i1 %3)
+    // DBG-NOT: icmp
+    // DBG-NOT: assume
+    // CHECK: %[[P1:.+]] = insertvalue { i32, i32 } poison, i32 %x.0, 0
+    // CHECK: %[[P2:.+]] = insertvalue { i32, i32 } %[[P1]], i32 %x.1, 1
+    // CHECK: ret { i32, i32 } %[[P2]]
+
+    transmute(x)
+}
+
+// CHECK-LABEL: @check_bool_from_ordering(
+#[no_mangle]
+pub unsafe fn check_bool_from_ordering(x: std::cmp::Ordering) -> bool {
+    // OPT: %0 = icmp uge i8 %x, -1
+    // OPT: %1 = icmp ule i8 %x, 1
+    // OPT: %2 = or i1 %0, %1
+    // OPT: call void @llvm.assume(i1 %2)
+    // OPT: %3 = icmp ule i8 %x, 1
+    // OPT: call void @llvm.assume(i1 %3)
+    // DBG-NOT: icmp
+    // DBG-NOT: assume
+    // CHECK: %[[R:.+]] = trunc i8 %x to i1
+    // CHECK: ret i1 %[[R]]
+
+    transmute(x)
+}
+
+// CHECK-LABEL: @check_bool_to_ordering(
+#[no_mangle]
+pub unsafe fn check_bool_to_ordering(x: bool) -> std::cmp::Ordering {
+    // CHECK: %0 = zext i1 %x to i8
+    // OPT: %1 = icmp ule i8 %0, 1
+    // OPT: call void @llvm.assume(i1 %1)
+    // OPT: %2 = icmp uge i8 %0, -1
+    // OPT: %3 = icmp ule i8 %0, 1
+    // OPT: %4 = or i1 %2, %3
+    // OPT: call void @llvm.assume(i1 %4)
+    // DBG-NOT: icmp
+    // DBG-NOT: assume
+    // CHECK: ret i8 %0
+
+    transmute(x)
+}

tests/codegen/intrinsics/transmute.rs

@@ -169,8 +169,8 @@ pub unsafe fn check_aggregate_from_bool(x: bool) -> Aggregate8 {
 #[no_mangle]
 pub unsafe fn check_byte_to_bool(x: u8) -> bool {
     // CHECK-NOT: alloca
-    // CHECK: %0 = trunc i8 %x to i1
-    // CHECK: ret i1 %0
+    // CHECK: %[[R:.+]] = trunc i8 %x to i1
+    // CHECK: ret i1 %[[R]]
     transmute(x)
 }
 
@@ -178,8 +178,8 @@ pub unsafe fn check_byte_to_bool(x: u8) -> bool {
 #[no_mangle]
 pub unsafe fn check_byte_from_bool(x: bool) -> u8 {
     // CHECK-NOT: alloca
-    // CHECK: %0 = zext i1 %x to i8
-    // CHECK: ret i8 %0
+    // CHECK: %[[R:.+]] = zext i1 %x to i8
+    // CHECK: ret i8 %[[R:.+]]
     transmute(x)
 }
 

tests/codegen/transmute-optimized.rs

@@ -0,0 +1,109 @@
+// compile-flags: -O -Z merge-functions=disabled
+// min-llvm-version: 15.0 # this test uses `ptr`s
+// ignore-debug
+
+#![crate_type = "lib"]
+
+// This tests that LLVM can optimize based on the niches in the source or
+// destination types for transmutes.
+
+#[repr(u32)]
+pub enum AlwaysZero32 { X = 0 }
+
+// CHECK-LABEL: i32 @issue_109958(i32
+#[no_mangle]
+pub fn issue_109958(x: AlwaysZero32) -> i32 {
+    // CHECK: ret i32 0
+    unsafe { std::mem::transmute(x) }
+}
+
+// CHECK-LABEL: i1 @reference_is_null(ptr
+#[no_mangle]
+pub fn reference_is_null(x: &i32) -> bool {
+    // CHECK: ret i1 false
+    let p: *const i32 = unsafe { std::mem::transmute(x) };
+    p.is_null()
+}
+
+// CHECK-LABEL: i1 @non_null_is_null(ptr
+#[no_mangle]
+pub fn non_null_is_null(x: std::ptr::NonNull<i32>) -> bool {
+    // CHECK: ret i1 false
+    let p: *const i32 = unsafe { std::mem::transmute(x) };
+    p.is_null()
+}
+
+// CHECK-LABEL: i1 @non_zero_is_null(
+#[no_mangle]
+pub fn non_zero_is_null(x: std::num::NonZeroUsize) -> bool {
+    // CHECK: ret i1 false
+    let p: *const i32 = unsafe { std::mem::transmute(x) };
+    p.is_null()
+}
+
+// CHECK-LABEL: i1 @non_null_is_zero(ptr
+#[no_mangle]
+pub fn non_null_is_zero(x: std::ptr::NonNull<i32>) -> bool {
+    // CHECK: ret i1 false
+    let a: isize = unsafe { std::mem::transmute(x) };
+    a == 0
+}
+
+// CHECK-LABEL: i1 @bool_ordering_is_ge(i1
+#[no_mangle]
+pub fn bool_ordering_is_ge(x: bool) -> bool {
+    // CHECK: ret i1 true
+    let y: std::cmp::Ordering = unsafe { std::mem::transmute(x) };
+    y.is_ge()
+}
+
+// CHECK-LABEL: i1 @ordering_is_ge_then_transmute_to_bool(i8
+#[no_mangle]
+pub fn ordering_is_ge_then_transmute_to_bool(x: std::cmp::Ordering) -> bool {
+    let r = x.is_ge();
+    let _: bool = unsafe { std::mem::transmute(x) };
+    r
+}
+
+// CHECK-LABEL: i32 @normal_div(i32
+#[no_mangle]
+pub fn normal_div(a: u32, b: u32) -> u32 {
+    // CHECK: call core::panicking::panic
+    a / b
+}
+
+// CHECK-LABEL: i32 @div_transmute_nonzero(i32
+#[no_mangle]
+pub fn div_transmute_nonzero(a: u32, b: std::num::NonZeroI32) -> u32 {
+    // CHECK-NOT: call core::panicking::panic
+    // CHECK: %[[R:.+]] = udiv i32 %a, %b
+    // CHECK-NEXT: ret i32 %[[R]]
+    // CHECK-NOT: call core::panicking::panic
+    let d: u32 = unsafe { std::mem::transmute(b) };
+    a / d
+}
+
+#[repr(i8)]
+pub enum OneTwoThree { One = 1, Two = 2, Three = 3 }
+
+// CHECK-LABEL: i8 @ordering_transmute_onetwothree(i8
+#[no_mangle]
+pub unsafe fn ordering_transmute_onetwothree(x: std::cmp::Ordering) -> OneTwoThree {
+    // CHECK: ret i8 1
+    std::mem::transmute(x)
+}
+
+// CHECK-LABEL: i8 @onetwothree_transmute_ordering(i8
+#[no_mangle]
+pub unsafe fn onetwothree_transmute_ordering(x: OneTwoThree) -> std::cmp::Ordering {
+    // CHECK: ret i8 1
+    std::mem::transmute(x)
+}
+
+// CHECK-LABEL: i1 @char_is_negative(i32
+#[no_mangle]
+pub fn char_is_negative(c: char) -> bool {
+    // CHECK: ret i1 false
+    let x: i32 = unsafe { std::mem::transmute(c) };
+    x < 0
+}

tests/codegen/transmute-scalar.rs

@@ -1,4 +1,4 @@
-// compile-flags: -O -C no-prepopulate-passes
+// compile-flags: -C opt-level=0 -C no-prepopulate-passes
 // min-llvm-version: 15.0 # this test assumes `ptr`s and thus no `pointercast`s
 
 #![crate_type = "lib"]
@@ -10,7 +10,7 @@
 // However, `bitcast`s and `ptrtoint`s and `inttoptr`s are still worth doing when
 // that allows us to avoid the `alloca`s entirely; see `rvalue_creates_operand`.
 
-// CHECK-LABEL: define{{.*}}i32 @f32_to_bits(float noundef %x)
+// CHECK-LABEL: define{{.*}}i32 @f32_to_bits(float %x)
 // CHECK: %0 = bitcast float %x to i32
 // CHECK-NEXT: ret i32 %0
 #[no_mangle]
@@ -18,7 +18,7 @@ pub fn f32_to_bits(x: f32) -> u32 {
     unsafe { std::mem::transmute(x) }
 }
 
-// CHECK-LABEL: define{{.*}}i8 @bool_to_byte(i1 noundef zeroext %b)
+// CHECK-LABEL: define{{.*}}i8 @bool_to_byte(i1 zeroext %b)
 // CHECK: %0 = zext i1 %b to i8
 // CHECK-NEXT: ret i8 %0
 #[no_mangle]
@@ -26,7 +26,7 @@ pub fn bool_to_byte(b: bool) -> u8 {
     unsafe { std::mem::transmute(b) }
 }
 
-// CHECK-LABEL: define{{.*}}noundef zeroext i1 @byte_to_bool(i8 noundef %byte)
+// CHECK-LABEL: define{{.*}}zeroext i1 @byte_to_bool(i8 %byte)
 // CHECK: %0 = trunc i8 %byte to i1
 // CHECK-NEXT: ret i1 %0
 #[no_mangle]
@@ -34,14 +34,14 @@ pub unsafe fn byte_to_bool(byte: u8) -> bool {
     std::mem::transmute(byte)
 }
 
-// CHECK-LABEL: define{{.*}}ptr @ptr_to_ptr(ptr noundef %p)
+// CHECK-LABEL: define{{.*}}ptr @ptr_to_ptr(ptr %p)
 // CHECK: ret ptr %p
 #[no_mangle]
 pub fn ptr_to_ptr(p: *mut u16) -> *mut u8 {
     unsafe { std::mem::transmute(p) }
 }
 
-// CHECK: define{{.*}}[[USIZE:i[0-9]+]] @ptr_to_int(ptr noundef %p)
+// CHECK: define{{.*}}[[USIZE:i[0-9]+]] @ptr_to_int(ptr %p)
 // CHECK: %0 = ptrtoint ptr %p to [[USIZE]]
 // CHECK-NEXT: ret [[USIZE]] %0
 #[no_mangle]
@@ -49,7 +49,7 @@ pub fn ptr_to_int(p: *mut u16) -> usize {
     unsafe { std::mem::transmute(p) }
 }
 
-// CHECK: define{{.*}}ptr @int_to_ptr([[USIZE]] noundef %i)
+// CHECK: define{{.*}}ptr @int_to_ptr([[USIZE]] %i)
 // CHECK: %0 = inttoptr [[USIZE]] %i to ptr
 // CHECK-NEXT: ret ptr %0
 #[no_mangle]