[MLIR][LLVM] Add inline_hint as a first class function attribute (llvm#163324)

We have `noinline` and `alwaysinline` present as first class function
attributes. Add `inline_hint` to the list of function attributes as
well.

Update the module import and translation to support the new attribute.

The verifier does not need to be changed as `inlinehint` does not
conflict with `noinline` or `alwaysinline`.

`inline_hint` is needed to support the `inline` C/C++ keyword in CIR.

Author: mmha

mlir/include/mlir/Dialect/LLVMIR/LLVMOps.td

@@ -1986,6 +1986,7 @@ def LLVM_LLVMFuncOp : LLVM_Op<"func", [
     OptionalAttr<StrAttr>:$instrument_function_exit,
     OptionalAttr<UnitAttr>:$no_inline,
     OptionalAttr<UnitAttr>:$always_inline,
+    OptionalAttr<UnitAttr>:$inline_hint,
     OptionalAttr<UnitAttr>:$no_unwind,
     OptionalAttr<UnitAttr>:$will_return,
     OptionalAttr<UnitAttr>:$optimize_none,
@@ -2038,6 +2039,9 @@ def LLVM_LLVMFuncOp : LLVM_Op<"func", [
     /// Returns true if the `always_inline` attribute is set, false otherwise.
     bool isAlwaysInline() { return bool(getAlwaysInlineAttr()); }
 
+    /// Returns true if the `inline_hint` attribute is set, false otherwise.
+    bool isInlineHint() { return bool(getInlineHintAttr()); }
+
     /// Returns true if the `optimize_none` attribute is set, false otherwise.
     bool isOptimizeNone() { return bool(getOptimizeNoneAttr()); }
   }];

mlir/lib/Target/LLVMIR/ModuleImport.cpp

@@ -2604,6 +2604,7 @@ static constexpr std::array kExplicitLLVMFuncOpAttributes{
     StringLiteral("denormal-fp-math-f32"),
     StringLiteral("fp-contract"),
     StringLiteral("frame-pointer"),
+    StringLiteral("inlinehint"),
     StringLiteral("instrument-function-entry"),
     StringLiteral("instrument-function-exit"),
     StringLiteral("memory"),
@@ -2643,6 +2644,8 @@ void ModuleImport::processFunctionAttributes(llvm::Function *func,
     funcOp.setNoInline(true);
   if (func->hasFnAttribute(llvm::Attribute::AlwaysInline))
     funcOp.setAlwaysInline(true);
+  if (func->hasFnAttribute(llvm::Attribute::InlineHint))
+    funcOp.setInlineHint(true);
   if (func->hasFnAttribute(llvm::Attribute::OptimizeNone))
     funcOp.setOptimizeNone(true);
   if (func->hasFnAttribute(llvm::Attribute::Convergent))

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

@@ -1652,6 +1652,8 @@ static void convertFunctionAttributes(LLVMFuncOp func,
     llvmFunc->addFnAttr(llvm::Attribute::NoInline);
   if (func.getAlwaysInlineAttr())
     llvmFunc->addFnAttr(llvm::Attribute::AlwaysInline);
+  if (func.getInlineHintAttr())
+    llvmFunc->addFnAttr(llvm::Attribute::InlineHint);
   if (func.getOptimizeNoneAttr())
     llvmFunc->addFnAttr(llvm::Attribute::OptimizeNone);
   if (func.getConvergentAttr())

mlir/test/Target/LLVMIR/Import/function-attributes.ll

@@ -393,6 +393,12 @@ declare void @alwaysinline_attribute() alwaysinline
 
 // -----
 
+; CHECK-LABEL: @inlinehint_attribute
+; CHECK-SAME: attributes {inline_hint}
+declare void @inlinehint_attribute() inlinehint
+
+// -----
+
 ; CHECK-LABEL: @optnone_attribute
 ; CHECK-SAME: attributes {no_inline, optimize_none}
 declare void @optnone_attribute() noinline optnone

mlir/test/Target/LLVMIR/llvmir.mlir

@@ -2555,6 +2555,17 @@ llvm.func @always_inline() attributes { always_inline } {
 
 // -----
 
+// CHECK-LABEL: @inline_hint
+// CHECK-SAME: #[[ATTRS:[0-9]+]]
+llvm.func @inline_hint() attributes { inline_hint } {
+  llvm.return
+}
+
+// CHECK: #[[ATTRS]]
+// CHECK-SAME: inlinehint
+
+// -----
+
 // CHECK-LABEL: @optimize_none
 // CHECK-SAME: #[[ATTRS:[0-9]+]]
 llvm.func @optimize_none() attributes { no_inline, optimize_none } {