[CIR][CIRGen] Implement constant evaluation for integral builtins (#381)

Author: philnik777

clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp

@@ -52,7 +52,12 @@ RValue CIRGenFunction::buildBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
   Expr::EvalResult Result;
   if (E->isPRValue() && E->EvaluateAsRValue(Result, CGM.getASTContext()) &&
       !Result.hasSideEffects()) {
-    llvm_unreachable("NYI");
+    if (Result.Val.isInt()) {
+      return RValue::get(builder.getConstInt(getLoc(E->getSourceRange()),
+                                             Result.Val.getInt()));
+    }
+    if (Result.Val.isFloat())
+      llvm_unreachable("NYI");
   }
 
   // If current long-double semantics is IEEE 128-bit, replace math builtins

clang/test/CIR/CodeGen/builtin-constant-evaluated.cpp

@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-unknown-linux-gnu -fclangir-enable -emit-cir %s -o - | FileCheck %s
+
+auto func() {
+  return __builtin_strcmp("", "");
+  // CHECK:      cir.func @_Z4funcv() -> !s32i extra( {inline = #cir.inline<no>, optnone = #cir.optnone} ) {
+  // CHECK-NEXT: %0 = cir.alloca !s32i, cir.ptr <!s32i>, ["__retval"] {alignment = 4 : i64} loc(#loc2)
+  // CHECK-NEXT: %1 = cir.const(#cir.int<0> : !s32i) : !s32i loc(#loc7)
+  // CHECK-NEXT: cir.store %1, %0 : !s32i, cir.ptr <!s32i> loc(#loc8)
+  // CHECK-NEXT: %2 = cir.load %0 : cir.ptr <!s32i>, !s32i loc(#loc8)
+  // CHECK-NEXT: cir.return %2 : !s32i loc(#loc8)
+}