[CIR] Add support for __builtin_assume (#144376)

This patch adds support for the `__builtin_assume` builtin function.

Author: Lancern

clang/include/clang/CIR/Dialect/IR/CIROps.td

@@ -2387,4 +2387,26 @@ def ComplexCreateOp : CIR_Op<"complex.create", [Pure, SameTypeOperands]> {
   let hasFolder = 1;
 }
 
+//===----------------------------------------------------------------------===//
+// Assume Operations
+//===----------------------------------------------------------------------===//
+
+def AssumeOp : CIR_Op<"assume"> {
+  let summary = "Tell the optimizer that a boolean value is true";
+  let description = [{
+    The `cir.assume` operation takes a single boolean prediate as its only
+    argument and does not have any results. The operation tells the optimizer
+    that the predicate is always true.
+
+    This operation corresponds to the `__assume` and the `__builtin_assume`
+    builtin functions.
+  }];
+
+  let arguments = (ins CIR_BoolType:$predicate);
+
+  let assemblyFormat = [{
+    $predicate `:` type($predicate) attr-dict
+  }];
+}
+
 #endif // CLANG_CIR_DIALECT_IR_CIROPS_TD

clang/include/clang/CIR/MissingFeatures.h

@@ -237,6 +237,9 @@ struct MissingFeatures {
   static bool lowerAggregateLoadStore() { return false; }
   static bool dataLayoutTypeAllocSize() { return false; }
   static bool asmLabelAttr() { return false; }
+  static bool builtinCall() { return false; }
+  static bool builtinCallF128() { return false; }
+  static bool builtinCallMathErrno() { return false; }
 
   // Missing types
   static bool dataMemberType() { return false; }

clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp

@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "CIRGenCall.h"
+#include "CIRGenConstantEmitter.h"
 #include "CIRGenFunction.h"
 #include "CIRGenModule.h"
 #include "CIRGenValue.h"
@@ -66,6 +67,32 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
     return emitLibraryCall(*this, fd, e,
                            cgm.getBuiltinLibFunction(fd, builtinID));
 
+  assert(!cir::MissingFeatures::builtinCallF128());
+
+  // If the builtin has been declared explicitly with an assembler label,
+  // disable the specialized emitting below. Ideally we should communicate the
+  // rename in IR, or at least avoid generating the intrinsic calls that are
+  // likely to get lowered to the renamed library functions.
+  unsigned builtinIDIfNoAsmLabel = fd->hasAttr<AsmLabelAttr>() ? 0 : builtinID;
+
+  assert(!cir::MissingFeatures::builtinCallMathErrno());
+  assert(!cir::MissingFeatures::builtinCall());
+
+  switch (builtinIDIfNoAsmLabel) {
+  default:
+    break;
+
+  case Builtin::BI__assume:
+  case Builtin::BI__builtin_assume: {
+    if (e->getArg(0)->HasSideEffects(getContext()))
+      return RValue::get(nullptr);
+
+    mlir::Value argValue = emitCheckedArgForAssume(e->getArg(0));
+    builder.create<cir::AssumeOp>(getLoc(e->getExprLoc()), argValue);
+    return RValue::get(nullptr);
+  }
+  }
+
   cgm.errorNYI(e->getSourceRange(), "unimplemented builtin call");
   return getUndefRValue(e->getType());
 }
@@ -88,3 +115,14 @@ cir::FuncOp CIRGenModule::getBuiltinLibFunction(const FunctionDecl *fd,
   mlir::Type type = convertType(fd->getType());
   return getOrCreateCIRFunction(name, type, d, /*forVTable=*/false);
 }
+
+mlir::Value CIRGenFunction::emitCheckedArgForAssume(const Expr *e) {
+  mlir::Value argValue = evaluateExprAsBool(e);
+  if (!sanOpts.has(SanitizerKind::Builtin))
+    return argValue;
+
+  assert(!cir::MissingFeatures::sanitizers());
+  cgm.errorNYI(e->getSourceRange(),
+               "emitCheckedArgForAssume: sanitizers are NYI");
+  return {};
+}

clang/lib/CIR/CodeGen/CIRGenFunction.h

@@ -772,6 +772,10 @@ class CIRGenFunction : public CIRGenTypeCache {
 
   LValue emitCastLValue(const CastExpr *e);
 
+  /// Emits an argument for a call to a `__builtin_assume`. If the builtin
+  /// sanitizer is enabled, a runtime check is also emitted.
+  mlir::Value emitCheckedArgForAssume(const Expr *e);
+
   LValue emitCompoundAssignmentLValue(const clang::CompoundAssignOperator *e);
 
   void emitConstructorBody(FunctionArgList &args);

clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp

@@ -407,6 +407,14 @@ struct ConvertCIRToLLVMPass
   StringRef getArgument() const override { return "cir-flat-to-llvm"; }
 };
 
+mlir::LogicalResult CIRToLLVMAssumeOpLowering::matchAndRewrite(
+    cir::AssumeOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  auto cond = adaptor.getPredicate();
+  rewriter.replaceOpWithNewOp<mlir::LLVM::AssumeOp>(op, cond);
+  return mlir::success();
+}
+
 mlir::LogicalResult CIRToLLVMBrCondOpLowering::matchAndRewrite(
     cir::BrCondOp brOp, OpAdaptor adaptor,
     mlir::ConversionPatternRewriter &rewriter) const {
@@ -1811,6 +1819,7 @@ void ConvertCIRToLLVMPass::runOnOperation() {
                                              dl);
   patterns.add<
       // clang-format off
+               CIRToLLVMAssumeOpLowering,
                CIRToLLVMBaseClassAddrOpLowering,
                CIRToLLVMBinOpLowering,
                CIRToLLVMBrCondOpLowering,

clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h

@@ -29,6 +29,16 @@ mlir::Value lowerCirAttrAsValue(mlir::Operation *parentOp, mlir::Attribute attr,
 
 mlir::LLVM::Linkage convertLinkage(cir::GlobalLinkageKind linkage);
 
+class CIRToLLVMAssumeOpLowering
+    : public mlir::OpConversionPattern<cir::AssumeOp> {
+public:
+  using mlir::OpConversionPattern<cir::AssumeOp>::OpConversionPattern;
+
+  mlir::LogicalResult
+  matchAndRewrite(cir::AssumeOp op, OpAdaptor,
+                  mlir::ConversionPatternRewriter &) const override;
+};
+
 class CIRToLLVMBrCondOpLowering
     : public mlir::OpConversionPattern<cir::BrCondOp> {
 public:

clang/test/CIR/CodeGen/builtin_call.cpp

@@ -94,3 +94,19 @@ void library_builtins() {
 // OGCG: define dso_local void @_Z16library_builtinsv()
 // OGCG: call i32 (ptr, ...) @printf(ptr noundef null)
 // OGCG: call void @abort()
+
+void assume(bool arg) {
+  __builtin_assume(arg);
+}
+
+// CIR: cir.func @_Z6assumeb
+// CIR:   cir.assume %{{.+}} : !cir.bool
+// CIR: }
+
+// LLVM: define void @_Z6assumeb
+// LLVM:   call void @llvm.assume(i1 %{{.+}})
+// LLVM: }
+
+// OGCG: define {{.*}}void @_Z6assumeb
+// OGCG:   call void @llvm.assume(i1 %{{.+}})
+// OGCG: }