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Correct implementation of shift and rotate.

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The existing implementations worked on x86-64 when instructions were emitted, but relied on UB per the LLVM IR. Add a test which checks the behaviour when the inputs are constants, so that the LLVM IR constant folder can see and exploit the UB.
This commit is contained in:
Nick Lewycky
2021-03-01 15:00:18 -08:00
parent 64baed9337
commit c422fdeba2
2 changed files with 222 additions and 11 deletions
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64
lib/compiler-llvm/src/translator/code.rs
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@ -2818,12 +2818,23 @@ impl<'ctx, 'a> LLVMFunctionCodeGenerator<'ctx, 'a> {
let res = self.builder.build_bitcast(res, self.intrinsics.i128_ty, "");
self.state.push1(res);
}
Operator::I32Shl | Operator::I64Shl => {
Operator::I32Shl => {
let ((v1, i1), (v2, i2)) = self.state.pop2_extra()?;
let v1 = self.apply_pending_canonicalization(v1, i1);
let v2 = self.apply_pending_canonicalization(v2, i2);
let (v1, v2) = (v1.into_int_value(), v2.into_int_value());
// TODO: missing 'and' of v2?
let mask = self.intrinsics.i32_ty.const_int(31u64, false);
let v2 = self.builder.build_and(v2, mask, "");
let res = self.builder.build_left_shift(v1, v2, "");
self.state.push1(res);
}
Operator::I64Shl => {
let ((v1, i1), (v2, i2)) = self.state.pop2_extra()?;
let v1 = self.apply_pending_canonicalization(v1, i1);
let v2 = self.apply_pending_canonicalization(v2, i2);
let (v1, v2) = (v1.into_int_value(), v2.into_int_value());
let mask = self.intrinsics.i32_ty.const_int(63u64, false);
let v2 = self.builder.build_and(v2, mask, "");
let res = self.builder.build_left_shift(v1, v2, "");
self.state.push1(res);
}
@ -2888,12 +2899,23 @@ impl<'ctx, 'a> LLVMFunctionCodeGenerator<'ctx, 'a> {
let res = self.builder.build_bitcast(res, self.intrinsics.i128_ty, "");
self.state.push1(res);
}
Operator::I32ShrS | Operator::I64ShrS => {
Operator::I32ShrS => {
let ((v1, i1), (v2, i2)) = self.state.pop2_extra()?;
let v1 = self.apply_pending_canonicalization(v1, i1);
let v2 = self.apply_pending_canonicalization(v2, i2);
let (v1, v2) = (v1.into_int_value(), v2.into_int_value());
// TODO: check wasm spec, is this missing v2 mod LaneBits?
let mask = self.intrinsics.i32_ty.const_int(31u64, false);
let v2 = self.builder.build_and(v2, mask, "");
let res = self.builder.build_right_shift(v1, v2, true, "");
self.state.push1(res);
}
Operator::I64ShrS => {
let ((v1, i1), (v2, i2)) = self.state.pop2_extra()?;
let v1 = self.apply_pending_canonicalization(v1, i1);
let v2 = self.apply_pending_canonicalization(v2, i2);
let (v1, v2) = (v1.into_int_value(), v2.into_int_value());
let mask = self.intrinsics.i32_ty.const_int(63u64, false);
let v2 = self.builder.build_and(v2, mask, "");
let res = self.builder.build_right_shift(v1, v2, true, "");
self.state.push1(res);
}
@ -2958,11 +2980,23 @@ impl<'ctx, 'a> LLVMFunctionCodeGenerator<'ctx, 'a> {
let res = self.builder.build_bitcast(res, self.intrinsics.i128_ty, "");
self.state.push1(res);
}
Operator::I32ShrU | Operator::I64ShrU => {
Operator::I32ShrU => {
let ((v1, i1), (v2, i2)) = self.state.pop2_extra()?;
let v1 = self.apply_pending_canonicalization(v1, i1);
let v2 = self.apply_pending_canonicalization(v2, i2);
let (v1, v2) = (v1.into_int_value(), v2.into_int_value());
let mask = self.intrinsics.i32_ty.const_int(31u64, false);
let v2 = self.builder.build_and(v2, mask, "");
let res = self.builder.build_right_shift(v1, v2, false, "");
self.state.push1(res);
}
Operator::I64ShrU => {
let ((v1, i1), (v2, i2)) = self.state.pop2_extra()?;
let v1 = self.apply_pending_canonicalization(v1, i1);
let v2 = self.apply_pending_canonicalization(v2, i2);
let (v1, v2) = (v1.into_int_value(), v2.into_int_value());
let mask = self.intrinsics.i32_ty.const_int(63u64, false);
let v2 = self.builder.build_and(v2, mask, "");
let res = self.builder.build_right_shift(v1, v2, false, "");
self.state.push1(res);
}
@ -3032,10 +3066,12 @@ impl<'ctx, 'a> LLVMFunctionCodeGenerator<'ctx, 'a> {
let v1 = self.apply_pending_canonicalization(v1, i1);
let v2 = self.apply_pending_canonicalization(v2, i2);
let (v1, v2) = (v1.into_int_value(), v2.into_int_value());
let mask = self.intrinsics.i32_ty.const_int(31u64, false);
let v2 = self.builder.build_and(v2, mask, "");
let lhs = self.builder.build_left_shift(v1, v2, "");
let rhs = {
let int_width = self.intrinsics.i32_ty.const_int(32 as u64, false);
let rhs = self.builder.build_int_sub(int_width, v2, "");
let negv2 = self.builder.build_int_neg(v2, "");
let rhs = self.builder.build_and(negv2, mask, "");
self.builder.build_right_shift(v1, rhs, false, "")
};
let res = self.builder.build_or(lhs, rhs, "");
@ -3046,10 +3082,12 @@ impl<'ctx, 'a> LLVMFunctionCodeGenerator<'ctx, 'a> {
let v1 = self.apply_pending_canonicalization(v1, i1);
let v2 = self.apply_pending_canonicalization(v2, i2);
let (v1, v2) = (v1.into_int_value(), v2.into_int_value());
let mask = self.intrinsics.i32_ty.const_int(63u64, false);
let v2 = self.builder.build_and(v2, mask, "");
let lhs = self.builder.build_left_shift(v1, v2, "");
let rhs = {
let int_width = self.intrinsics.i64_ty.const_int(64 as u64, false);
let rhs = self.builder.build_int_sub(int_width, v2, "");
let negv2 = self.builder.build_int_neg(v2, "");
let rhs = self.builder.build_and(negv2, mask, "");
self.builder.build_right_shift(v1, rhs, false, "")
};
let res = self.builder.build_or(lhs, rhs, "");
@ -3060,10 +3098,12 @@ impl<'ctx, 'a> LLVMFunctionCodeGenerator<'ctx, 'a> {
let v1 = self.apply_pending_canonicalization(v1, i1);
let v2 = self.apply_pending_canonicalization(v2, i2);
let (v1, v2) = (v1.into_int_value(), v2.into_int_value());
let mask = self.intrinsics.i32_ty.const_int(31u64, false);
let v2 = self.builder.build_and(v2, mask, "");
let lhs = self.builder.build_right_shift(v1, v2, false, "");
let rhs = {
let int_width = self.intrinsics.i32_ty.const_int(32 as u64, false);
let rhs = self.builder.build_int_sub(int_width, v2, "");
let negv2 = self.builder.build_int_neg(v2, "");
let rhs = self.builder.build_and(negv2, mask, "");
self.builder.build_left_shift(v1, rhs, "")
};
let res = self.builder.build_or(lhs, rhs, "");
@ -3074,6 +3114,8 @@ impl<'ctx, 'a> LLVMFunctionCodeGenerator<'ctx, 'a> {
let v1 = self.apply_pending_canonicalization(v1, i1);
let v2 = self.apply_pending_canonicalization(v2, i2);
let (v1, v2) = (v1.into_int_value(), v2.into_int_value());
let mask = self.intrinsics.i32_ty.const_int(63u64, false);
let v2 = self.builder.build_and(v2, mask, "");
let lhs = self.builder.build_right_shift(v1, v2, false, "");
let rhs = {
let int_width = self.intrinsics.i64_ty.const_int(64 as u64, false);