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Improve codegen for unchecked float casts on wasm #74659

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merged 1 commit into from
Jul 23, 2020
Merged

Improve codegen for unchecked float casts on wasm #74659

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8 changes: 8 additions & 0 deletions src/librustc_codegen_llvm/context.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -510,6 +510,14 @@ impl CodegenCx<'b, 'tcx> {
ifn!("llvm.wasm.trunc.saturate.signed.i32.f64", fn(t_f64) -> t_i32);
ifn!("llvm.wasm.trunc.saturate.signed.i64.f32", fn(t_f32) -> t_i64);
ifn!("llvm.wasm.trunc.saturate.signed.i64.f64", fn(t_f64) -> t_i64);
ifn!("llvm.wasm.trunc.unsigned.i32.f32", fn(t_f32) -> t_i32);
ifn!("llvm.wasm.trunc.unsigned.i32.f64", fn(t_f64) -> t_i32);
ifn!("llvm.wasm.trunc.unsigned.i64.f32", fn(t_f32) -> t_i64);
ifn!("llvm.wasm.trunc.unsigned.i64.f64", fn(t_f64) -> t_i64);
ifn!("llvm.wasm.trunc.signed.i32.f32", fn(t_f32) -> t_i32);
ifn!("llvm.wasm.trunc.signed.i32.f64", fn(t_f64) -> t_i32);
ifn!("llvm.wasm.trunc.signed.i64.f32", fn(t_f32) -> t_i64);
ifn!("llvm.wasm.trunc.signed.i64.f64", fn(t_f64) -> t_i64);

ifn!("llvm.trap", fn() -> void);
ifn!("llvm.debugtrap", fn() -> void);
Expand Down
75 changes: 57 additions & 18 deletions src/librustc_codegen_llvm/intrinsic.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -629,27 +629,24 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
}

sym::float_to_int_unchecked => {
if float_type_width(arg_tys[0]).is_none() {
span_invalid_monomorphization_error(
tcx.sess,
span,
&format!(
"invalid monomorphization of `float_to_int_unchecked` \
let float_width = match float_type_width(arg_tys[0]) {
Some(width) => width,
None => {
span_invalid_monomorphization_error(
tcx.sess,
span,
&format!(
"invalid monomorphization of `float_to_int_unchecked` \
intrinsic: expected basic float type, \
found `{}`",
arg_tys[0]
),
);
return;
}
match int_type_width_signed(ret_ty, self.cx) {
Some((width, signed)) => {
if signed {
self.fptosi(args[0].immediate(), self.cx.type_ix(width))
} else {
self.fptoui(args[0].immediate(), self.cx.type_ix(width))
}
arg_tys[0]
),
);
return;
}
};
let (width, signed) = match int_type_width_signed(ret_ty, self.cx) {
Some(pair) => pair,
None => {
span_invalid_monomorphization_error(
tcx.sess,
Expand All @@ -663,7 +660,49 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
);
return;
}
};

// The LLVM backend can reorder and speculate `fptosi` and
// `fptoui`, so on WebAssembly the codegen for this instruction
// is quite heavyweight. To avoid this heavyweight codegen we
// instead use the raw wasm intrinsics which will lower to one
// instruction in WebAssembly (`iNN.trunc_fMM_{s,u}`). This one
// instruction will trap if the operand is out of bounds, but
// that's ok since this intrinsic is UB if the operands are out
// of bounds, so the behavior can be different on WebAssembly
// than other targets.
//
// Note, however, that when the `nontrapping-fptoint` feature is
// enabled in LLVM then LLVM will lower `fptosi` to
// `iNN.trunc_sat_fMM_{s,u}`, so if that's the case we don't
// bother with intrinsics.
let mut result = None;
if self.sess().target.target.arch == "wasm32"
&& !self.sess().target_features.contains(&sym::nontrapping_dash_fptoint)
{
let name = match (width, float_width, signed) {
(32, 32, true) => Some("llvm.wasm.trunc.signed.i32.f32"),
(32, 64, true) => Some("llvm.wasm.trunc.signed.i32.f64"),
(64, 32, true) => Some("llvm.wasm.trunc.signed.i64.f32"),
(64, 64, true) => Some("llvm.wasm.trunc.signed.i64.f64"),
(32, 32, false) => Some("llvm.wasm.trunc.unsigned.i32.f32"),
(32, 64, false) => Some("llvm.wasm.trunc.unsigned.i32.f64"),
(64, 32, false) => Some("llvm.wasm.trunc.unsigned.i64.f32"),
(64, 64, false) => Some("llvm.wasm.trunc.unsigned.i64.f64"),
_ => None,
};
if let Some(name) = name {
let intrinsic = self.get_intrinsic(name);
result = Some(self.call(intrinsic, &[args[0].immediate()], None));
}
}
result.unwrap_or_else(|| {
if signed {
self.fptosi(args[0].immediate(), self.cx.type_ix(width))
} else {
self.fptoui(args[0].immediate(), self.cx.type_ix(width))
}
})
}

sym::discriminant_value => {
Expand Down
1 change: 1 addition & 0 deletions src/test/codegen/unchecked-float-casts.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
// unchecked intrinsics.

// compile-flags: -C opt-level=3
// ignore-wasm32 the wasm target is tested in `wasm_casts_*`

#![crate_type = "lib"]

Expand Down
28 changes: 8 additions & 20 deletions src/test/codegen/wasm_casts_trapping.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,6 @@ pub fn cast_f32_i32(a: f32) -> i32 {
a as _
}


// CHECK-LABEL: @cast_f64_u64
#[no_mangle]
pub fn cast_f64_u64(a: f64) -> u64 {
Expand Down Expand Up @@ -84,77 +83,66 @@ pub fn cast_f32_u8(a: f32) -> u8 {
a as _
}



// CHECK-LABEL: @cast_unchecked_f64_i64
#[no_mangle]
pub unsafe fn cast_unchecked_f64_i64(a: f64) -> i64 {
// CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
// CHECK: fptosi double {{.*}} to i64
// CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.signed.{{.*}}
// CHECK-NEXT: ret i64 {{.*}}
a.to_int_unchecked()
}

// CHECK-LABEL: @cast_unchecked_f64_i32
#[no_mangle]
pub unsafe fn cast_unchecked_f64_i32(a: f64) -> i32 {
// CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
// CHECK: fptosi double {{.*}} to i32
// CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.signed.{{.*}}
// CHECK-NEXT: ret i32 {{.*}}
a.to_int_unchecked()
}

// CHECK-LABEL: @cast_unchecked_f32_i64
#[no_mangle]
pub unsafe fn cast_unchecked_f32_i64(a: f32) -> i64 {
// CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
// CHECK: fptosi float {{.*}} to i64
// CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.signed.{{.*}}
// CHECK-NEXT: ret i64 {{.*}}
a.to_int_unchecked()
}

// CHECK-LABEL: @cast_unchecked_f32_i32
#[no_mangle]
pub unsafe fn cast_unchecked_f32_i32(a: f32) -> i32 {
// CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
// CHECK: fptosi float {{.*}} to i32
// CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.signed.{{.*}}
// CHECK-NEXT: ret i32 {{.*}}
a.to_int_unchecked()
}


// CHECK-LABEL: @cast_unchecked_f64_u64
#[no_mangle]
pub unsafe fn cast_unchecked_f64_u64(a: f64) -> u64 {
// CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
// CHECK: fptoui double {{.*}} to i64
// CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.unsigned.{{.*}}
// CHECK-NEXT: ret i64 {{.*}}
a.to_int_unchecked()
}

// CHECK-LABEL: @cast_unchecked_f64_u32
#[no_mangle]
pub unsafe fn cast_unchecked_f64_u32(a: f64) -> u32 {
// CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
// CHECK: fptoui double {{.*}} to i32
// CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.unsigned.{{.*}}
// CHECK-NEXT: ret i32 {{.*}}
a.to_int_unchecked()
}

// CHECK-LABEL: @cast_unchecked_f32_u64
#[no_mangle]
pub unsafe fn cast_unchecked_f32_u64(a: f32) -> u64 {
// CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
// CHECK: fptoui float {{.*}} to i64
// CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.unsigned.{{.*}}
// CHECK-NEXT: ret i64 {{.*}}
a.to_int_unchecked()
}

// CHECK-LABEL: @cast_unchecked_f32_u32
#[no_mangle]
pub unsafe fn cast_unchecked_f32_u32(a: f32) -> u32 {
// CHECK-NOT: {{.*}} call {{.*}} @llvm.wasm.trunc.{{.*}}
// CHECK: fptoui float {{.*}} to i32
// CHECK: {{.*}} call {{.*}} @llvm.wasm.trunc.unsigned.{{.*}}
// CHECK-NEXT: ret i32 {{.*}}
a.to_int_unchecked()
}
Expand Down