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Implement black_box using intrinsic

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The new implementation allows some `memcpy`s to be optimized away,
so the uninit value in ui/sanitize/memory.rs is constructed directly
onto the return place. Therefore the sanitizer now says that the
value is allocated by `main` rather than `random`.
This commit is contained in:
Gary Guo 2021-08-10 11:50:33 +01:00
parent ae90dcf020
commit 1fb1643129
9 changed files with 52 additions and 15 deletions
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26
compiler/rustc_codegen_llvm/src/intrinsic.rs
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@ -7,6 +7,7 @@ use crate::type_of::LayoutLlvmExt;
use crate::va_arg::emit_va_arg;
use crate::value::Value;
use rustc_ast as ast;
use rustc_codegen_ssa::base::{compare_simd_types, wants_msvc_seh};
use rustc_codegen_ssa::common::span_invalid_monomorphization_error;
use rustc_codegen_ssa::common::{IntPredicate, TypeKind};
@ -327,6 +328,31 @@ impl IntrinsicCallMethods<'tcx> for Builder<'a, 'll, 'tcx> {
}
}
sym::black_box => {
args[0].val.store(self, result);
// We need to "use" the argument in some way LLVM can't introspect, and on
// targets that support it we can typically leverage inline assembly to do
// this. LLVM's interpretation of inline assembly is that it's, well, a black
// box. This isn't the greatest implementation since it probably deoptimizes
// more than we want, but it's so far good enough.
crate::asm::inline_asm_call(
self,
"",
"r,~{memory}",
&[result.llval],
self.type_void(),
true,
false,
ast::LlvmAsmDialect::Att,
&[span],
)
.unwrap_or_else(|| bug!("failed to generate inline asm call for `black_box`"));
// We have copied the value to `result` already.
return;
}
_ if name_str.starts_with("simd_") => {
match generic_simd_intrinsic(self, name, callee_ty, args, ret_ty, llret_ty, span) {
Ok(llval) => llval,