Rollup merge of #119365 - nbdd0121:asm-goto, r=Amanieu

Add asm goto support to `asm!`

Tracking issue: #119364

This PR implements asm-goto support, using the syntax described in "future possibilities" section of [RFC2873](https://rust-lang.github.io/rfcs/2873-inline-asm.html#asm-goto).

Currently I have only implemented the `label` part, not the `fallthrough` part (i.e. fallthrough is implicit). This doesn't reduce the expressive though, since you can use label-break to get arbitrary control flow or simply set a value and rely on jump threading optimisation to get the desired control flow. I can add that later if deemed necessary.

r? ``@Amanieu``
cc ``@ojeda``

compiler/rustc_codegen_llvm/src/asm.rs

@@ -28,7 +28,8 @@ impl<'ll, 'tcx> AsmBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
         options: InlineAsmOptions,
         line_spans: &[Span],
         instance: Instance<'_>,
-        dest_catch_funclet: Option<(Self::BasicBlock, Self::BasicBlock, Option<&Self::Funclet>)>,
+        dest: Option<Self::BasicBlock>,
+        catch_funclet: Option<(Self::BasicBlock, Option<&Self::Funclet>)>,
     ) {
         let asm_arch = self.tcx.sess.asm_arch.unwrap();
 
@@ -165,6 +166,7 @@ impl<'ll, 'tcx> AsmBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
         }
 
         // Build the template string
+        let mut labels = vec![];
         let mut template_str = String::new();
         for piece in template {
             match *piece {
@@ -205,6 +207,11 @@ impl<'ll, 'tcx> AsmBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
                             // Only emit the raw symbol name
                             template_str.push_str(&format!("${{{}:c}}", op_idx[&operand_idx]));
                         }
+                        InlineAsmOperandRef::Label { label } => {
+                            template_str.push_str(&format!("${{{}:l}}", constraints.len()));
+                            constraints.push("!i".to_owned());
+                            labels.push(label);
+                        }
                     }
                 }
             }
@@ -292,12 +299,14 @@ impl<'ll, 'tcx> AsmBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
             &constraints.join(","),
             &inputs,
             output_type,
+            &labels,
             volatile,
             alignstack,
             dialect,
             line_spans,
             options.contains(InlineAsmOptions::MAY_UNWIND),
-            dest_catch_funclet,
+            dest,
+            catch_funclet,
         )
         .unwrap_or_else(|| span_bug!(line_spans[0], "LLVM asm constraint validation failed"));
 
@@ -317,7 +326,7 @@ impl<'ll, 'tcx> AsmBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
         attributes::apply_to_callsite(result, llvm::AttributePlace::Function, &{ attrs });
 
         // Switch to the 'normal' basic block if we did an `invoke` instead of a `call`
-        if let Some((dest, _, _)) = dest_catch_funclet {
+        if let Some(dest) = dest {
             self.switch_to_block(dest);
         }
 
@@ -415,16 +424,14 @@ pub(crate) fn inline_asm_call<'ll>(
     cons: &str,
     inputs: &[&'ll Value],
     output: &'ll llvm::Type,
+    labels: &[&'ll llvm::BasicBlock],
     volatile: bool,
     alignstack: bool,
     dia: llvm::AsmDialect,
     line_spans: &[Span],
     unwind: bool,
-    dest_catch_funclet: Option<(
-        &'ll llvm::BasicBlock,
-        &'ll llvm::BasicBlock,
-        Option<&Funclet<'ll>>,
-    )>,
+    dest: Option<&'ll llvm::BasicBlock>,
+    catch_funclet: Option<(&'ll llvm::BasicBlock, Option<&Funclet<'ll>>)>,
 ) -> Option<&'ll Value> {
     let volatile = if volatile { llvm::True } else { llvm::False };
     let alignstack = if alignstack { llvm::True } else { llvm::False };
@@ -457,8 +464,11 @@ pub(crate) fn inline_asm_call<'ll>(
                 can_throw,
             );
 
-            let call = if let Some((dest, catch, funclet)) = dest_catch_funclet {
-                bx.invoke(fty, None, None, v, inputs, dest, catch, funclet)
+            let call = if !labels.is_empty() {
+                assert!(catch_funclet.is_none());
+                bx.callbr(fty, None, None, v, inputs, dest.unwrap(), labels, None)
+            } else if let Some((catch, funclet)) = catch_funclet {
+                bx.invoke(fty, None, None, v, inputs, dest.unwrap(), catch, funclet)
             } else {
                 bx.call(fty, None, None, v, inputs, None)
             };

compiler/rustc_codegen_llvm/src/builder.rs

@@ -1538,6 +1538,58 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
         }
     }
 
+    pub(crate) fn callbr(
+        &mut self,
+        llty: &'ll Type,
+        fn_attrs: Option<&CodegenFnAttrs>,
+        fn_abi: Option<&FnAbi<'tcx, Ty<'tcx>>>,
+        llfn: &'ll Value,
+        args: &[&'ll Value],
+        default_dest: &'ll BasicBlock,
+        indirect_dest: &[&'ll BasicBlock],
+        funclet: Option<&Funclet<'ll>>,
+    ) -> &'ll Value {
+        debug!("invoke {:?} with args ({:?})", llfn, args);
+
+        let args = self.check_call("callbr", llty, llfn, args);
+        let funclet_bundle = funclet.map(|funclet| funclet.bundle());
+        let funclet_bundle = funclet_bundle.as_ref().map(|b| &*b.raw);
+        let mut bundles: SmallVec<[_; 2]> = SmallVec::new();
+        if let Some(funclet_bundle) = funclet_bundle {
+            bundles.push(funclet_bundle);
+        }
+
+        // Emit CFI pointer type membership test
+        self.cfi_type_test(fn_attrs, fn_abi, llfn);
+
+        // Emit KCFI operand bundle
+        let kcfi_bundle = self.kcfi_operand_bundle(fn_attrs, fn_abi, llfn);
+        let kcfi_bundle = kcfi_bundle.as_ref().map(|b| &*b.raw);
+        if let Some(kcfi_bundle) = kcfi_bundle {
+            bundles.push(kcfi_bundle);
+        }
+
+        let callbr = unsafe {
+            llvm::LLVMRustBuildCallBr(
+                self.llbuilder,
+                llty,
+                llfn,
+                default_dest,
+                indirect_dest.as_ptr(),
+                indirect_dest.len() as c_uint,
+                args.as_ptr(),
+                args.len() as c_uint,
+                bundles.as_ptr(),
+                bundles.len() as c_uint,
+                UNNAMED,
+            )
+        };
+        if let Some(fn_abi) = fn_abi {
+            fn_abi.apply_attrs_callsite(self, callbr);
+        }
+        callbr
+    }
+
     // Emits CFI pointer type membership tests.
     fn cfi_type_test(
         &mut self,

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -448,12 +448,14 @@ impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
                     constraint,
                     inputs,
                     self.type_void(),
+                    &[],
                     true,
                     false,
                     llvm::AsmDialect::Att,
                     &[span],
                     false,
                     None,
+                    None,
                 )
                 .unwrap_or_else(|| bug!("failed to generate inline asm call for `black_box`"));
 

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -1616,6 +1616,20 @@ extern "C" {
         Name: *const c_char,
     ) -> &'a Value;
 
+    pub fn LLVMRustBuildCallBr<'a>(
+        B: &Builder<'a>,
+        Ty: &'a Type,
+        Fn: &'a Value,
+        DefaultDest: &'a BasicBlock,
+        IndirectDests: *const &'a BasicBlock,
+        NumIndirectDests: c_uint,
+        Args: *const &'a Value,
+        NumArgs: c_uint,
+        OpBundles: *const &OperandBundleDef<'a>,
+        NumOpBundles: c_uint,
+        Name: *const c_char,
+    ) -> &'a Value;
+
     pub fn LLVMRustSetFastMath(Instr: &Value);
     pub fn LLVMRustSetAlgebraicMath(Instr: &Value);
     pub fn LLVMRustSetAllowReassoc(Instr: &Value);