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Fix local.set and local.tee types for SIMD

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Because Wasm SIMD vectors store their type as `v128`, there is a mismatch between the more specific types Cranelift uses and Wasm SIMD. Because of this mismatch, Wasm SIMD translates to the default Cranelift type `I8X16`, causing issues when more specific type information is available (e.g. `I32x4`). To fix this, all incoming values to SIMD instructions are checked during translation (not runtime) and if necessary cast from `I8X16` to the appropriate type by functions like `optionally_bitcast_vector`, `pop1_with_bitcast` and `pop2_with_bitcast`. However, there are times when we must also cast to `I8X16` for outgoing values, as with `local.set` and `local.tee`.

There are other ways of resolving this (e.g., see adding a new vector type, https://github.com/bytecodealliance/cranelift/pull/1251) but we discussed staying with this casting approach in https://github.com/bytecodealliance/wasmtime/issues/1147.
This commit is contained in:
Andrew Brown
2020-03-13 15:11:41 -07:00
parent 8bbf07c758
commit 27532410d2
2 changed files with 22 additions and 2 deletions
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18
cranelift/wasm/src/code_translator.rs
View File

@@ -73,13 +73,27 @@ pub fn translate_operator<FE: FuncEnvironment + ?Sized>(
builder.set_val_label(val, label);
}
Operator::LocalSet { local_index } => {
let val = state.pop1();
let mut val = state.pop1();
// Ensure SIMD values are cast to their default Cranelift type, I8x16.
let ty = builder.func.dfg.value_type(val);
if ty.is_vector() {
val = optionally_bitcast_vector(val, I8X16, builder);
}
builder.def_var(Variable::with_u32(*local_index), val);
let label = ValueLabel::from_u32(*local_index);
builder.set_val_label(val, label);
}
Operator::LocalTee { local_index } => {
let val = state.peek1();
let mut val = state.peek1();
// Ensure SIMD values are cast to their default Cranelift type, I8x16.
let ty = builder.func.dfg.value_type(val);
if ty.is_vector() {
val = optionally_bitcast_vector(val, I8X16, builder);
}
builder.def_var(Variable::with_u32(*local_index), val);
let label = ValueLabel::from_u32(*local_index);
builder.set_val_label(val, label);

6
cranelift/wasmtests/simd.wat
View File

@@ -17,6 +17,12 @@
i32x4.extract_lane 3
)
(func $test_locals (local i32 v128)
local.get 0
i32x4.splat
local.set 1
)
(export "test_splat" (func $test_splat))
(export "test_insert_lane" (func $test_insert_lane))
(export "test_const" (func $test_const))