[CIR][CIRGen] Support __builtin_huge_val for float type (#889)

as title. 
The test cases are from [clang codegen test
case](https://github.com/llvm/clangir/blob/52323c17c6a3708b3eb72651465f7d4b82f057e7/clang/test/CodeGen/builtins.c#L37)

Author: ghehg

clang/lib/CIR/CodeGen/CIRGenBuilder.h

@@ -536,6 +536,15 @@ class CIRGenBuilderTy : public CIRBaseBuilderTy {
 
   mlir::cir::ConstantOp getConstInt(mlir::Location loc, mlir::Type t,
                                     uint64_t C);
+
+  mlir::cir::ConstantOp getConstFP(mlir::Location loc, mlir::Type t,
+                                   llvm::APFloat fpVal) {
+    assert((mlir::isa<mlir::cir::SingleType, mlir::cir::DoubleType>(t)) &&
+           "expected mlir::cir::SingleType or mlir::cir::DoubleType");
+    return create<mlir::cir::ConstantOp>(loc, t,
+                                         getAttr<mlir::cir::FPAttr>(t, fpVal));
+  }
+
   /// Create constant nullptr for pointer-to-data-member type ty.
   mlir::cir::ConstantOp getNullDataMemberPtr(mlir::cir::DataMemberType ty,
                                              mlir::Location loc) {

clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp

@@ -313,8 +313,16 @@ RValue CIRGenFunction::buildBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
       return RValue::get(builder.getConstInt(getLoc(E->getSourceRange()),
                                              Result.Val.getInt()));
     }
-    if (Result.Val.isFloat())
-      llvm_unreachable("NYI");
+    if (Result.Val.isFloat()) {
+      // Note: we are using result type of CallExpr to determine the type of
+      // the constant. Clang Codegen uses the result value to make judgement
+      // of the type. We feel it should be Ok to use expression type because
+      // it is hard to imagine a builtin function evaluates to
+      // a value that over/underflows its own defined type.
+      mlir::Type resTy = getCIRType(E->getType());
+      return RValue::get(builder.getConstFP(getLoc(E->getExprLoc()), resTy,
+                                            Result.Val.getFloat()));
+    }
   }
 
   // If current long-double semantics is IEEE 128-bit, replace math builtins

clang/test/CIR/CodeGen/builtins.c

@@ -0,0 +1,28 @@
+// RUN: %clang_cc1 -triple aarch64-none-linux-android21 -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck -check-prefix=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -triple aarch64-none-linux-android21 -fclangir -emit-llvm %s -o %t.ll
+// RUN: FileCheck --check-prefix=LLVM --input-file=%t.ll %s
+
+
+void test1() {
+  float f;
+  double d;
+  f = __builtin_huge_valf();    
+  d = __builtin_huge_val();
+}
+
+// CIR-LABEL: test1
+// CIR: [[F:%.*]] = cir.alloca !cir.float, !cir.ptr<!cir.float>, ["f"] {alignment = 4 : i64} 
+// CIR: [[D:%.*]] = cir.alloca !cir.double, !cir.ptr<!cir.double>, ["d"] {alignment = 8 : i64}
+// CIR: [[F_VAL:%.*]] = cir.const #cir.fp<0x7F800000> : !cir.float 
+// CIR: cir.store [[F_VAL]], [[F]] : !cir.float, !cir.ptr<!cir.float> 
+// CIR: [[D_VAL:%.*]] = cir.const #cir.fp<0x7FF0000000000000> : !cir.double 
+// CIR: cir.store [[D_VAL]], [[D]] : !cir.double, !cir.ptr<!cir.double> loc(#loc17)
+// CIR: cir.return
+
+// LLVM-LABEL: test1
+// [[F:%.*]] = alloca float, align 4
+// [[D:%.*]] = alloca double, align 8
+// store float 0x7FF0000000000000, ptr [[F]], align 4
+// store double 0x7FF0000000000000, ptr[[D]], align 8
+// ret void